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Kidney Diseases Dataset – Renal Disorders & Conditions Database
Kidney Diseases Dataset
The Kidney Diseases Dataset is a structured medical database containing a comprehensive list of conditions affecting the kidneys and urinary system.
Kidney diseases can significantly impact overall health, as the kidneys play a vital role in filtering waste, balancing fluids, and regulating essential body functions. Conditions range from common infections to chronic kidney disease and renal failure.
This dataset provides organised information to support medical research, healthcare analytics, and application development.
Each record includes key clinical details such as disease descriptions, affected renal structures, common symptoms, severity levels, and treatment approaches.
The dataset has been cleaned and structured for easy integration into spreadsheets, databases, and analytical tools.
It is ideal for nephrology research, healthcare developers, educators, and data scientists working with renal health data.
Dataset Contents
The dataset includes fields such as:
- Disease / Condition Name
- Description
- Affected Area (Kidneys, Nephrons, Urinary System)
- Common Symptoms
- Severity Level
- Disease Category
- Risk Factors
- Treatment / Management
Example Conditions Included
- Chronic Kidney Disease (CKD)
- Acute Kidney Injury (AKI)
- Kidney Stones (Nephrolithiasis)
- Glomerulonephritis
- Polycystic Kidney Disease
- Nephrotic Syndrome
- Urinary Tract Infection (UTI)
- Renal Failure
- Hydronephrosis
- Diabetic Nephropathy
...and many more kidney-related conditions.
Data Preview
12 columns
25 rows shown
| No. | Disease Name | Category | Primary Cause / Etiology | Prevalence | Age of Onset | Key Symptoms | Affected Organ(s) | Diagnostic Method | Treatment Approach | Prognosis | ICD-10 Code | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | ▸ Glomerular Diseases | |||||||||||
| 2 | 1 | ANCA-Associated Vasculitis (Renal) | Glomerular Diseases | ANCA-associated vasculitis (AAV) encompasses granulomatosis with polyangiitis (GPA, formerly Wegener's), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA, formerly Churg-Strauss), all of which can cause pauci-immune necrotizing and crescentic glomerulonephritis. The pathogenesis involves anti-neutrophil cytoplasmic antibodies directed against proteinase 3 (PR3-ANCA, more common in GPA) or myeloperoxidase (MPO-ANCA, more common in MPA and EGPA). ANCA activate primed neutrophils by binding to PR3 or MPO expressed on the neutrophil surface, triggering degranulation, release of reactive oxygen species, and formation of neutrophil extracellular traps (NETs). Activated neutrophils adhere to glomerular endothelium, causing necrotizing vasculitis of glomerular capillaries with fibrinoid necrosis, GBM rupture, and crescent formation. The pauci-immune pattern (absence of significant immunoglobulin deposits) distinguishes AAV from immune complex-mediated crescentic GN. Alternative complement pathway activation through C5a-C5aR axis amplifies neutrophil recruitment and plays a critical role in disease pathogenesis, providing the rationale for complement-targeted therapies. Environmental triggers including silica exposure, infections, and certain medications (hydralazine, propylthiouracil, levamisole-adulterated cocaine) have been associated with ANCA formation. | AAV has an annual incidence of approximately 15-25 per million and a prevalence of approximately 200-400 per million in Western countries. GPA and MPA are the most common forms, with GPA predominating in Northern Europe and MPA in Southern Europe and Asia. Renal involvement occurs in 70-85% of MPA and 40-60% of GPA patients. The mean age at diagnosis is 55-65 years, with a slight male predominance (1.5:1). AAV is more common in Caucasians, though it occurs in all racial groups. Renal involvement is a major determinant of morbidity and mortality and is the presenting feature in many patients. AAV accounts for approximately 3-5% of ESRD. | AAV predominantly affects middle-aged and elderly adults, with peak incidence in the sixth to seventh decades of life. It is uncommon in children but can occur at any age. PR3-ANCA positive GPA tends to present at a younger age (mean 50 years) than MPO-ANCA positive MPA (mean 60-65 years). Childhood AAV is rare but may present with more aggressive renal disease. Drug-induced ANCA vasculitis (e.g., from propylthiouracil) may occur at younger ages depending on medication exposure. | Renal manifestations range from asymptomatic urinary abnormalities to fulminant RPGN. Active urinary sediment with microscopic hematuria, dysmorphic RBCs, RBC casts, and proteinuria (usually non-nephrotic) is the hallmark. Rapidly progressive renal failure with rising creatinine over days to weeks occurs in 30-50% of patients at presentation. Hypertension is present in 30-50% but is often mild. Systemic symptoms include constitutional symptoms (fever, weight loss, fatigue, malaise) in 70-90% of patients. GPA-specific features include upper airway disease (sinusitis, epistaxis, saddle nose deformity, subglottic stenosis), pulmonary nodules or cavitary lesions, and orbital pseudotumor. MPA-specific features include diffuse alveolar hemorrhage (occurring in 10-30%) presenting with hemoptysis, dyspnea, and bilateral infiltrates. Skin manifestations (palpable purpura in 30-50%), peripheral neuropathy (mononeuritis multiplex in 20-30%), and musculoskeletal symptoms (arthralgia, myalgia) are common in both GPA and MPA. | Kidneys (glomeruli - pauci-immune necrotizing crescentic GN); lungs (alveolar hemorrhage, nodules, cavities); upper airways (sinuses, nasal septum, subglottic region); skin (purpura, ulcers); peripheral nerves (mononeuritis multiplex); eyes (scleritis, orbital pseudotumor); joints | ANCA testing by ELISA for PR3 and MPO antibodies is the initial diagnostic step, with sensitivity of 85-95% and specificity of >95% for active AAV with renal involvement. Renal biopsy is essential for confirming the diagnosis and assessing severity. Biopsy shows necrotizing and crescentic GN with pauci-immune immunofluorescence pattern (no or minimal immunoglobulin deposits). The Berden histologic classification grades renal biopsies into focal, crescentic, mixed, and sclerotic classes, with prognostic implications. Urinalysis shows active nephritic sediment. Chest CT evaluates for pulmonary involvement (nodules, cavities, ground-glass opacities). CRP and ESR are typically markedly elevated. Complete blood count may show anemia and leukocytosis. Serum creatinine at presentation and the percentage of normal glomeruli on biopsy are the strongest predictors of long-term renal outcome. | Induction therapy for severe AAV (organ-threatening, including renal involvement): rituximab (375 mg/m2 IV weekly x 4) is non-inferior and often preferred over cyclophosphamide based on RAVE and RITUXVAS trials, particularly for PR3-ANCA positive disease, relapsing disease, and when cyclophosphamide is contraindicated. Alternatively, IV cyclophosphamide (15 mg/kg every 2 weeks x 3, then every 3 weeks x 3-6, per Euro-Vasculitis Study Group protocol) combined with glucocorticoids. Avacopan (30 mg twice daily), a C5a receptor antagonist, is FDA-approved as add-on therapy replacing or reducing glucocorticoids based on the ADVOCATE trial showing superior sustained remission rates. IV methylprednisolone (500-1000 mg x 3 days) followed by oral prednisone (0.5-1 mg/kg/day tapered to off by 3-6 months). Plasma exchange is considered for severe disease with creatinine >5.8 mg/dL or pulmonary hemorrhage. Maintenance therapy: rituximab (500 mg IV every 6 months for at least 2-4 years) is preferred over azathioprine (2 mg/kg/day) based on MAINRITSAN trials. Trimethoprim-sulfamethoxazole (800/160 mg three times weekly) for Pneumocystis prophylaxis during immunosuppression. | Variable - With modern treatment, 1-year survival exceeds 85-90% and 5-year survival is 70-80%. Renal survival at 5 years is approximately 75-85% with prompt treatment. Complete remission is achieved in 70-90% with induction therapy. Relapse rates remain significant: 40-60% for PR3-ANCA positive disease and 20-30% for MPO-ANCA positive disease over 5 years without maintenance therapy; maintenance rituximab reduces relapse rates to 10-15%. Factors predicting poor renal outcome include high serum creatinine at diagnosis, high percentage of sclerotic glomeruli on biopsy, and delayed treatment. AAV accounts for approximately 3-5% of ESRD; dialysis-dependent patients at diagnosis have a 30-50% chance of renal recovery with aggressive treatment. Five-year transplant graft survival is comparable to other causes of ESRD (>85%), with relapse in transplant occurring in 10-15%. | M31.7 |
| 3 | 2 | Alport Syndrome | Glomerular Diseases | Alport syndrome is a hereditary nephritis caused by mutations in genes encoding type IV collagen alpha chains, specifically COL4A5 (X-linked form, 80% of cases), or COL4A3/COL4A4 (autosomal recessive form, 15%, and autosomal dominant form, 5%). The alpha-3, alpha-4, and alpha-5(IV) chains form the alpha-3-4-5(IV) collagen network, which is the major structural component of the mature GBM, cochlear basement membranes, and lens capsule. In Alport syndrome, mutations prevent proper assembly and incorporation of the alpha-3-4-5 network, and the GBM retains the fetal alpha-1-1-2(IV) network, which is thinner, more susceptible to proteolytic degradation, and less resistant to mechanical stress. The GBM progressively deteriorates, showing characteristic alternating thinning and thickening with lamellation and basket-weave splitting of the lamina densa on electron microscopy. This progressive GBM damage leads to hematuria, proteinuria, and eventual glomerulosclerosis with interstitial fibrosis. In the X-linked form, affected males (hemizygous) have more severe disease than affected females (heterozygous), who have a mosaic pattern of normal and abnormal GBM due to random X-inactivation. The same alpha-3-4-5(IV) network is present in the cochlear basement membrane and lens capsule, explaining the characteristic extrarenal manifestations of sensorineural hearing loss and ocular anomalies. | Alport syndrome affects approximately 1 in 5,000 to 1 in 10,000 people, accounting for approximately 1-2% of all ESRD. X-linked Alport syndrome (XLAS) accounts for approximately 80% of cases, autosomal recessive for 15%, and autosomal dominant for 5%. Males with XLAS inevitably develop ESRD, typically by age 20-30 (severe phenotype with truncating mutations) or by age 40-60 (milder phenotype with missense mutations). Approximately 12% of females heterozygous for XLAS develop ESRD, usually after age 40. Alport syndrome is found worldwide with no significant racial or ethnic predilection. | Microscopic hematuria is present from birth in males with XLAS and is typically the first manifestation. Proteinuria develops in the first to second decade. Sensorineural hearing loss typically becomes detectable in late childhood to early adolescence (age 6-15) in severe XLAS. Renal failure develops in the second to third decade in severe XLAS (truncating mutations) and in the fourth to fifth decade in milder forms (missense mutations). Females with XLAS may develop hematuria and proteinuria at any age. Autosomal recessive Alport syndrome presents similarly to severe XLAS in both sexes. | Persistent microscopic hematuria from birth is the earliest manifestation in affected males and is present in nearly 100% of XLAS males. Episodes of gross hematuria triggered by upper respiratory infections occur in 60-70% during childhood. Progressive proteinuria develops over the first to second decade, eventually reaching nephrotic range in many patients. Bilateral sensorineural hearing loss (initially high-frequency, eventually affecting conversational frequencies) develops in 80-90% of XLAS males, typically becoming clinically apparent between ages 6 and 15. Anterior lenticonus (conical protrusion of the anterior lens capsule, pathognomonic for Alport syndrome) is found in 15-30% of XLAS males and may cause progressive myopia. Perimacular retinal flecks (dot-and-fleck retinopathy) are found in 40-60%. Hypertension develops as CKD progresses. Progressive CKD manifests with fatigue, growth retardation, anemia, and uremic symptoms. Heterozygous XLAS females have a spectrum from asymptomatic hematuria to progressive CKD. | Kidneys (GBM - progressive deterioration and sclerosis); cochlea (sensorineural hearing loss); eyes (anterior lenticonus, retinal flecks, posterior polymorphous corneal dystrophy); rarely leiomyomatosis of esophagus and tracheobronchial tree (associated with COL4A5-COL4A6 deletions) | Genetic testing of COL4A3, COL4A4, and COL4A5 is the gold standard for diagnosis and should be performed first-line in suspected cases. Renal biopsy shows non-specific findings on light microscopy in early stages but progressive glomerulosclerosis and interstitial fibrosis in advanced disease. Electron microscopy demonstrates the characteristic GBM changes: alternating thinning and thickening with lamellation and basket-weave splitting of the lamina densa. Immunohistochemistry of the biopsy or skin biopsy for type IV collagen alpha chains is useful: in XLAS males, alpha-5(IV) is absent from the GBM and Bowman's capsule, and alpha-3 and alpha-4 are also absent from the GBM. In XLAS females, alpha-5(IV) staining is mosaic. Audiometry should be performed at diagnosis and regularly thereafter to monitor hearing loss. Ophthalmologic examination for anterior lenticonus and retinal flecks. Urinalysis shows persistent hematuria and progressive proteinuria. Family pedigree analysis helps determine the inheritance pattern. | ACE inhibitors are the cornerstone of therapy and should be initiated at the earliest sign of proteinuria (even microalbuminuria), as they significantly delay progression to ESRD. Ramipril (2.5-10 mg daily, pediatric dose 0.05-0.1 mg/kg/day) has the strongest evidence from the EARLY PRO-TECT Alport trial, which showed that ACE inhibitor initiation before CKD stage 3 delays ESRD by an average of 10-13 years. ARBs (losartan 25-100 mg daily) may be used as alternatives. Addition of an ARB to an ACE inhibitor (dual RAS blockade) is used by some centers for persistent proteinuria, though this approach is debated. Aldosterone receptor antagonists (spironolactone 25-50 mg daily or eplerenone 25-50 mg daily) may provide additional antiproteinuric benefit when added to ACE inhibitor/ARB therapy. SGLT2 inhibitors (dapagliflozin 10 mg daily) are increasingly being studied in Alport syndrome. Hearing aids are prescribed for significant hearing loss. Anterior lenticonus causing visual impairment may require lens replacement surgery. Kidney transplantation is the preferred renal replacement modality, with excellent outcomes and no recurrence of disease in the allograft; however, 3-5% of XLAS males develop post-transplant anti-GBM nephritis due to immune response against the 'novel' alpha-3-4-5(IV) network in the allograft. | Moderate - Males with XLAS and truncating COL4A5 mutations develop ESRD by a median age of 25 years, while those with missense mutations develop ESRD by a median age of 40-50 years. Early ACE inhibitor therapy significantly improves prognosis, delaying ESRD by 10-13 years or more. Approximately 12% of heterozygous XLAS females develop ESRD, usually after age 40, and up to 40% develop CKD. Autosomal recessive Alport syndrome progresses to ESRD by age 20-30 in both sexes. Hearing loss is progressive and bilateral; cochlear implants may be needed in severe cases. Kidney transplant outcomes are excellent (5-year graft survival >90%), with post-transplant anti-GBM disease occurring in 3-5% of XLAS males (most episodes are mild and self-limited). Gene therapy and chaperone therapy for Alport syndrome are in early research stages. | Q87.81 |
| 4 | 3 | Anti-GBM Disease (Goodpasture Syndrome) | Glomerular Diseases | Anti-glomerular basement membrane (anti-GBM) disease is a rare autoimmune condition caused by circulating autoantibodies directed against the non-collagenous 1 (NC1) domain of the alpha-3 chain of type IV collagen, a structural component of the glomerular and alveolar basement membranes. The target epitopes (designated EA and EB) are normally sequestered within the collagen IV hexameric network and become accessible through environmental triggers including pulmonary injury from cigarette smoking, inhaled hydrocarbons, cocaine, infections, or high oxygen concentrations. The anti-GBM antibodies (predominantly IgG1 and IgG3 subclasses) bind the alpha-3(IV)NC1 domain in a linear pattern along the GBM, activate complement via the classical pathway (C1q, C3, C5b-9), recruit neutrophils and monocytes, and cause severe necrotizing and crescentic glomerulonephritis. Pulmonary hemorrhage occurs when anti-GBM antibodies also bind the alveolar basement membrane, which is more accessible when the alveolar-capillary barrier is disrupted (explaining the association with smoking and hydrocarbon exposure). When both renal and pulmonary involvement are present, it is termed Goodpasture syndrome. Strong HLA association exists with HLA-DRB1*1501 (relative risk 8-16). The disease may overlap with ANCA positivity (double-positive disease) in 20-30% of cases. | Anti-GBM disease is rare, with an incidence of approximately 0.5-1.0 per million per year. It accounts for less than 5% of all crescentic glomerulonephritis and approximately 1-2% of all glomerulonephritis in biopsy series. There is a bimodal age distribution with peaks in the third decade (predominantly young males with pulmonary-renal disease) and sixth to seventh decades (predominantly renal-limited disease in both sexes). No significant racial or ethnic predilection has been established, though the disease appears rare in Sub-Saharan African populations. The disease may be triggered by environmental factors in genetically susceptible individuals. | Anti-GBM disease has a bimodal age distribution. The first peak occurs in young adults aged 20-30 years, predominantly males, who often present with pulmonary-renal syndrome (Goodpasture syndrome) and frequently have a history of smoking or hydrocarbon exposure. The second peak occurs in adults aged 60-70 years, with a more equal sex distribution, who more commonly present with renal-limited disease without pulmonary involvement. Pediatric cases are very rare. The elderly peak may overlap with ANCA-positive disease (double positivity). | Rapidly progressive glomerulonephritis is the hallmark, with rapidly rising serum creatinine, oliguria or anuria, and active urinary sediment with dysmorphic red blood cells and red blood cell casts developing over days to weeks. Pulmonary hemorrhage occurs in 40-60% of patients (Goodpasture syndrome), presenting with hemoptysis (ranging from mild to massive and life-threatening), dyspnea, cough, and diffuse alveolar infiltrates on chest imaging. Pulmonary hemorrhage may precede renal manifestations and can be fatal from asphyxiation. Constitutional symptoms including malaise, fatigue, weight loss, fever, and myalgias are common. Hypertension is variable and may be absent initially. Nausea, vomiting, and uremic symptoms develop rapidly in untreated patients. Anemia may be disproportionate to the degree of renal failure due to pulmonary blood loss. | Kidneys (glomerular basement membrane - crescentic GN); lungs (alveolar basement membrane - diffuse alveolar hemorrhage); rare involvement of choroid plexus, cochlea, and retina | Anti-GBM antibody testing (ELISA or chemiluminescent immunoassay) is the cornerstone of diagnosis, with sensitivity of 95-100% and specificity of >97%. False negatives may occur rarely, and if clinical suspicion is high despite negative serologic testing, renal biopsy should be performed. Renal biopsy shows necrotizing and crescentic glomerulonephritis with linear IgG deposition along the GBM on immunofluorescence (pathognomonic finding). Crescents are present in >50% (usually >80%) of glomeruli. ANCA testing should be performed simultaneously, as 20-30% of anti-GBM patients are double-positive (usually MPO-ANCA). Urinalysis shows nephritic sediment with dysmorphic RBCs, RBC casts, and proteinuria. Chest X-ray or CT shows bilateral alveolar infiltrates in pulmonary hemorrhage. Bronchoalveolar lavage (BAL) confirms alveolar hemorrhage with progressively hemorrhagic return and hemosiderin-laden macrophages. Serum creatinine at presentation is the strongest predictor of renal outcome. | Treatment is a medical emergency and should be initiated immediately upon clinical suspicion, before biopsy results are available. Plasmapheresis (daily 4L exchanges using 5% albumin replacement for 14 days or until anti-GBM antibodies are undetectable) rapidly removes circulating antibodies. Concurrent immunosuppressive therapy with IV methylprednisolone (500-1000 mg/day for 3 days) followed by oral prednisolone (1 mg/kg/day tapered over 6-9 months) and oral cyclophosphamide (2-3 mg/kg/day for 2-3 months) suppresses new antibody production. Rituximab (375 mg/m2 weekly x 4) may be used as an alternative to cyclophosphamide, particularly in patients with contraindications. Dialysis-dependent patients at presentation with 100% crescents on biopsy and no pulmonary hemorrhage have minimal chance of renal recovery (<5-8%), and aggressive immunosuppression may not be justified for renal benefit alone, though pulmonary hemorrhage still warrants treatment. Pulmonary hemorrhage is managed with supplemental oxygen, mechanical ventilation if needed, and avoidance of fluid overload. Smoking cessation and avoidance of hydrocarbon exposure are critical to prevent pulmonary hemorrhage recurrence. | Variable - Renal prognosis is heavily dependent on serum creatinine at presentation: patients presenting with creatinine <5.7 mg/dL have 80-90% renal survival at 1 year; those presenting with creatinine 5.7-7.5 mg/dL have 50-60% renal survival; those requiring dialysis at presentation have <8-15% chance of renal recovery. Pulmonary hemorrhage mortality has decreased from 50% to <10% with modern treatment but remains the primary cause of early death. With prompt and adequate treatment, patient survival exceeds 80-90% at 1 year. The disease is typically monophasic with less than 5% relapse rate (unlike ANCA vasculitis). Anti-GBM disease does not recur in kidney transplants if transplantation is delayed 6-12 months after antibodies become undetectable. Double-positive (anti-GBM + ANCA) patients may have a slightly better renal prognosis than anti-GBM alone but have higher relapse risk from the ANCA component. | M31.0 |
| 5 | 4 | C3 Glomerulopathy | Glomerular Diseases | C3 glomerulopathy (C3G) is a group of rare glomerular diseases defined by dominant C3 deposition on immunofluorescence with absent or scanty immunoglobulin staining, resulting from dysregulation of the alternative complement pathway. C3G comprises two entities based on electron microscopy findings: dense deposit disease (DDD, formerly MPGN type II) characterized by ribbon-like highly electron-dense intramembranous deposits transforming the GBM, and C3 glomerulonephritis (C3GN) characterized by mesangial and/or subendothelial deposits without the dense intramembranous deposits of DDD. The underlying pathogenesis involves uncontrolled activation of the alternative complement pathway, which may be caused by acquired autoantibodies (C3 nephritic factor/C3NeF in 50-80%, which stabilizes C3 convertase; anti-factor H antibodies in 10-15%) or by genetic mutations in complement regulatory genes (CFH in 10-20%, CFI, CFB, C3, CFHR gene rearrangements). The resulting persistent C3 activation and consumption leads to low serum C3 levels (found in 40-70% of patients) and C3 fragment deposition in glomeruli. Dense deposit disease derives its name from the osmiophilic transformation of the lamina densa of the GBM by C3 breakdown products. Monoclonal gammopathy may drive C3G through production of monoclonal immunoglobulins that interfere with complement regulation. | C3 glomerulopathy is very rare, with an estimated incidence of 1-2 per million per year. DDD is rarer than C3GN. C3G accounts for approximately 1-3% of all glomerulonephritis in renal biopsy series. It may be underdiagnosed, as some cases previously classified as MPGN or post-infectious GN may represent C3G. There is no significant gender predilection. C3G occurs in all ethnic groups. The association with monoclonal gammopathy increases with age, and patients over 50 should be screened for underlying paraproteinemia. | C3G can present at any age but has distinct age-related patterns. DDD predominantly presents in children and young adults (median age of diagnosis 10-15 years). C3GN presents more commonly in adults (median age 30-50 years). C3G associated with monoclonal gammopathy typically presents in adults over 50 years. The disease may present acutely or be discovered incidentally during evaluation of proteinuria or hematuria. | Clinical presentation is variable and non-specific. Proteinuria is present in nearly all patients, with nephrotic-range proteinuria in 30-50%. Microscopic hematuria is found in 70-90% of patients. Nephrotic syndrome (edema, hypoalbuminemia, hyperlipidemia) occurs in 30-50%. Acute nephritic syndrome with gross hematuria, hypertension, and renal impairment may be the presenting feature. Hypertension is present in 30-50%. Progressive CKD develops in many patients over time. Low serum C3 (reflecting alternative pathway consumption) is found in 40-70% of patients, while C4 is typically normal. DDD is uniquely associated with acquired partial lipodystrophy (loss of subcutaneous fat from the face and upper body) in 20-30% of cases, and retinal drusen (basal laminar deposits in Bruch's membrane) in 10-40%. | Kidneys (glomeruli - mesangium, GBM, capillary walls); eyes (retinal drusen in DDD); subcutaneous fat (acquired partial lipodystrophy in DDD); complement system (systemic alternative pathway dysregulation) | Renal biopsy is essential for diagnosis. Immunofluorescence shows dominant C3 deposition (C3 intensity ≥2 orders of magnitude greater than any immunoglobulin) with absent or scanty immunoglobulin staining. Light microscopy patterns vary and may include MPGN pattern (most common), mesangial proliferative, endocapillary proliferative, or crescentic patterns. Electron microscopy distinguishes DDD (pathognomonic dense intramembranous deposits) from C3GN (mesangial and subendothelial deposits). Serum C3 is low in 40-70% with normal C4 (alternative pathway). C3NeF is positive in 50-80% of DDD and 40-50% of C3GN. Anti-factor H antibodies should be tested. Serum and urine protein electrophoresis/immunofixation should be performed to exclude monoclonal gammopathy, especially in patients >50. Genetic testing of complement regulatory genes (CFH, CFI, CFB, C3, CFHR1-5) should be performed. Serum factor H, factor I, and factor B levels may be measured. Ophthalmologic examination for drusen is recommended in DDD. | There is no established standard therapy for C3G, and treatment is guided by limited evidence from case series and small studies. Supportive therapy with ACE inhibitors or ARBs for proteinuria and blood pressure control is the foundation. Mycophenolate mofetil (1-2 g/day) has shown benefit in observational studies, particularly for C3GN with active proliferative lesions. Corticosteroids alone have limited efficacy. Complement-targeted therapy with eculizumab (anti-C5 monoclonal antibody, 900 mg IV every 2 weeks) has shown variable results, with benefit primarily in patients with active proliferative disease and high C5b-9 levels. Iptacopan (LNP023, oral factor B inhibitor) and danicopan (factor D inhibitor) are under investigation in clinical trials for C3G. For C3G driven by monoclonal gammopathy, clone-directed therapy (rituximab for B-cell clones, bortezomib-based regimens for plasma cell clones) targeting the underlying dysproteinemia is essential. Plasma infusion (providing normal complement regulators) has been attempted in genetic factor H deficiency. Antiplatelet and anticoagulant therapy may be considered for MPGN-pattern disease. | Poor - C3G generally has a progressive course with significant risk of ESRD. DDD has a particularly poor prognosis, with approximately 50% of patients progressing to ESRD within 10 years. C3GN has a somewhat better prognosis but is still progressive, with 30-40% reaching ESRD by 10 years. Factors predicting poor outcome include crescentic histology, interstitial fibrosis, nephrotic-range proteinuria, and elevated creatinine at presentation. Post-transplant recurrence is very high, particularly for DDD (80-100% histologic recurrence, with 50% graft loss within 10 years) and C3GN (50-70% recurrence). Treatment of the underlying complement dysregulation (autoantibodies or genetic mutations) may improve transplant outcomes. Novel complement-targeted therapies offer hope for improved outcomes, but long-term efficacy data are awaited. | N05.8 |
| 6 | 5 | Collapsing Glomerulopathy | Glomerular Diseases | Collapsing glomerulopathy is a histologic variant of focal segmental glomerulosclerosis characterized by global or segmental collapse (wrinkling and retraction) of the glomerular capillary tuft with prominent hyperplasia and hypertrophy of overlying visceral epithelial cells (podocytes). Unlike other FSGS variants where podocytes are lost, collapsing glomerulopathy features podocyte dedifferentiation and proliferation, re-entering the cell cycle and losing mature podocyte markers (WT1, synaptopodin) while gaining proliferative markers (Ki-67, cyclin D1) and parietal epithelial cell markers. The etiology includes viral infections (HIV-1 is the prototypical cause, termed HIV-associated nephropathy/HIVAN; more recently SARS-CoV-2/COVID-19-associated collapsing glomerulopathy has been recognized), APOL1 high-risk genotypes (G1/G1, G1/G2, G2/G2, present in the vast majority of HIV-associated and idiopathic cases in African Americans), interferon therapy, bisphosphonate (pamidronate) use, and idiopathic causes. In HIVAN, HIV-1 directly infects podocytes and tubular epithelial cells, and viral gene products (Nef, Vpr) drive podocyte proliferation and apoptosis. The APOL1 risk variants encode gain-of-function protein that is toxic to podocytes through mechanisms involving mitochondrial dysfunction, inflammasome activation, and disruption of endolysosomal trafficking. Histologically, the collapsed capillary tuft is surrounded by swollen, vacuolated, proliferating podocytes that fill Bowman's space, creating the characteristic 'pseudocrescent' appearance. | Collapsing glomerulopathy is relatively uncommon but disproportionately affects individuals of African ancestry due to the high frequency of APOL1 risk variants (12-13% of African Americans carry two risk alleles). HIVAN historically occurred in 3-10% of HIV-infected African Americans before effective antiretroviral therapy (ART), and its incidence has decreased dramatically with widespread ART use. Idiopathic and viral-associated (non-HIV) collapsing glomerulopathy accounts for a smaller proportion. During the COVID-19 pandemic, collapsing glomerulopathy was reported as a complication of SARS-CoV-2 infection, almost exclusively in individuals with APOL1 high-risk genotypes. Collapsing FSGS accounts for approximately 10-15% of all FSGS cases in biopsy series. | HIVAN typically presents in adults aged 20-50 years, reflecting the demographics of HIV infection. Idiopathic collapsing glomerulopathy presents over a wider age range but most commonly in adults aged 30-50 years. COVID-19-associated collapsing glomerulopathy was reported in adults of all ages during the pandemic. The disease is rare in children but has been reported in perinatally HIV-infected children and in children with APOL1 high-risk genotypes. | Severe nephrotic syndrome with heavy proteinuria (often >10 g/day) is the hallmark presentation, typically with marked peripheral edema, anasarca, severe hypoalbuminemia (<2.0 g/dL), and hyperlipidemia. Rapid decline in renal function is characteristic, with elevated creatinine at presentation in 60-80% of patients. The combination of heavy proteinuria and renal insufficiency distinguishes collapsing glomerulopathy from minimal change disease clinically. Kidneys are typically enlarged (rather than small) on ultrasound due to parenchymal edema, which is an important distinguishing feature. Microscopic hematuria may be present. In HIVAN, the nephrotic syndrome may be the initial presentation of HIV infection, and HIV testing should be performed in any patient with collapsing FSGS. Systemic signs of HIV infection or COVID-19 may accompany the renal presentation. | Kidneys (podocytes - proliferation and dedifferentiation; glomerular capillary tuft - collapse); in HIVAN: also tubular epithelium (microcystic tubular dilation is characteristic), immune system | Renal biopsy is diagnostic. Light microscopy shows global or segmental collapse (wrinkling) of the glomerular capillary tuft with prominent podocyte hypertrophy and hyperplasia filling Bowman's space (pseudocrescents). Microcystic tubular dilation with proteinaceous casts is characteristic of HIVAN. Tubulointerstitial inflammation and fibrosis are often prominent. Immunofluorescence is typically negative or shows non-specific IgM/C3 trapping. Electron microscopy shows extensive podocyte foot process effacement, podocyte detachment, endothelial tubuloreticular inclusions (particularly in HIVAN, indicating interferon exposure), and absence of organized deposits. HIV testing (fourth-generation HIV-1/2 antigen/antibody combination test) should be performed in all cases of collapsing FSGS. APOL1 genotyping may be performed, particularly in patients of African ancestry. SARS-CoV-2 testing should be considered during pandemics. | For HIVAN, antiretroviral therapy (ART) is the cornerstone of treatment and should be initiated immediately; ART has dramatically reduced the incidence and improved the prognosis of HIVAN, converting it from a rapidly progressive disease to a manageable condition. ACE inhibitors or ARBs are recommended for proteinuria reduction in HIVAN. For non-HIV collapsing glomerulopathy, treatment is challenging and often disappointing. Immunosuppressive therapy with corticosteroids (prednisone 1 mg/kg/day), calcineurin inhibitors (cyclosporine 3-5 mg/kg/day or tacrolimus 0.05-0.1 mg/kg/day), or rituximab has been tried with limited success rates (20-40% partial remission). Supportive care with ACE inhibitors/ARBs, diuretics, and statin therapy is essential. For COVID-19-associated collapsing FSGS, treatment of the acute infection combined with supportive care is the primary approach. Given the role of APOL1 in disease pathogenesis, APOL1 inhibitors (inaxaplin) are in clinical development and represent a potential targeted therapy for APOL1-mediated kidney diseases. | Poor - Collapsing glomerulopathy has the worst prognosis among all FSGS variants. Without treatment, the median time to ESRD is approximately 1-2 years, with >50% reaching ESRD within 3 years. HIVAN prognosis has improved dramatically with ART, with renal survival increasing from <1 year (pre-ART era) to >5-10 years with effective viral suppression. Non-HIV collapsing FSGS remains highly resistant to therapy, with fewer than 30% achieving partial remission and >60% progressing to ESRD within 3-5 years. Post-transplant recurrence of idiopathic collapsing FSGS is high (30-50%), often occurring within days to weeks. APOL1 high-risk genotype in the recipient (but not the donor) is associated with worse graft outcomes. COVID-19-associated collapsing FSGS has variable outcomes, with some patients recovering renal function as the acute infection resolves. Novel APOL1-targeted therapies may transform the prognosis for APOL1-mediated collapsing glomerulopathy. | N04.1 |
| 7 | 6 | Dense Deposit Disease | Glomerular Diseases | Dense deposit disease (DDD, formerly MPGN type II) is a subtype of C3 glomerulopathy characterized by the pathognomonic presence of ribbon-like, highly electron-dense deposits within and transforming the lamina densa of the glomerular basement membrane. These deposits are composed primarily of C3 breakdown products (C3b, iC3b, C3dg) and complement membrane attack complex components, resulting from uncontrolled activation of the alternative complement pathway. The most common acquired driver is C3 nephritic factor (C3NeF), an IgG autoantibody that binds and stabilizes the alternative pathway C3 convertase (C3bBb), making it resistant to regulation by Factor H and increasing its half-life from minutes to hours. This leads to persistent, uncontrolled C3 activation, consumption of serum C3 (low C3 levels in 70-80% of patients), and massive deposition of C3 fragments along basement membranes throughout the body, including the GBM, tubular basement membranes, Bowman's capsule, and Bruch's membrane of the retina. Genetic mutations in complement regulatory genes (CFH, CFI, CFB, C3, CFHR gene rearrangements) are found in 20-30% of DDD patients. The dense deposits also occur in the choroid of the eye, causing drusen-like changes that differ from age-related macular degeneration drusen. Acquired partial lipodystrophy (Barraquer-Simons syndrome) occurs in 20-30% of DDD patients due to complement-mediated destruction of adipocytes. | DDD is very rare, with an estimated incidence of 2-3 per million per year in children and even lower in adults. It accounts for approximately 15-20% of all C3 glomerulopathy cases and is the rarer subtype compared to C3 glomerulonephritis. DDD predominantly affects children and young adults, with a median age of diagnosis of 10-15 years. There is no significant gender predilection. The disease is found worldwide but appears to be more commonly reported in Caucasian populations, which may reflect referral and biopsy patterns. | DDD predominantly presents in childhood, with a median age of diagnosis of approximately 10-15 years. The age range extends from early childhood to adulthood, though presentation after age 30 is uncommon. Retinal drusen may precede clinical renal disease by years. Acquired partial lipodystrophy may present in childhood or adolescence, sometimes preceding renal manifestations. | The clinical presentation is variable and may include nephrotic syndrome (proteinuria, edema, hypoalbuminemia in 30-50%), acute nephritic syndrome (hematuria, hypertension, renal impairment in 20-30%), or asymptomatic urinary abnormalities (microscopic hematuria and proteinuria in 20-30%). Gross hematuria may occur. Low serum C3 is found in 70-80% of patients, serving as an important diagnostic clue. Acquired partial lipodystrophy (progressive loss of subcutaneous fat from the face and upper body, with relative preservation of lower body fat) occurs in 20-30% and may be the initial presenting feature. Retinal drusen (round, yellowish deposits in the fundus) are found in 10-40% and may cause visual symptoms including metamorphopsia and scotomata. Progressive CKD develops over years in most patients. | Kidneys (GBM - dense intramembranous deposits; tubular basement membranes; Bowman's capsule); eyes (retinal drusen in Bruch's membrane); subcutaneous fat (acquired partial lipodystrophy); complement system (systemic alternative pathway dysregulation) | Renal biopsy is essential. Light microscopy most commonly shows an MPGN pattern with mesangial proliferation, GBM thickening, and double contours, though other patterns (mesangial proliferative, crescentic) may be seen. Immunofluorescence shows bright C3 deposition along the GBM and mesangium with absent or scanty immunoglobulin staining (C3-dominant pattern). Electron microscopy is diagnostic, demonstrating the pathognomonic ribbon-like, highly electron-dense transformation of the lamina densa of the GBM, extending continuously along capillary walls. Serum C3 is low in 70-80% with normal C4. C3NeF is positive in 60-80% of patients. Anti-Factor H antibodies should be tested. Genetic screening of complement genes (CFH, CFI, CFB, C3, CFHR1-5) is recommended. Ophthalmologic examination with optical coherence tomography (OCT) for drusen. Assessment for lipodystrophy with physical examination and body composition analysis. | There is no established disease-specific therapy for DDD, and treatment remains challenging. Supportive therapy with ACE inhibitors or ARBs for proteinuria and blood pressure control is the foundation. Mycophenolate mofetil (1-2 g/day in adults, 600 mg/m2/dose twice daily in children) has shown modest benefit in some cases. Eculizumab (anti-C5 monoclonal antibody, 900 mg IV every 2 weeks) has variable efficacy, with some reports of stabilization or improvement, particularly in patients with active proliferative disease. Novel complement inhibitors targeting the alternative pathway (iptacopan/factor B inhibitor, danicopan/factor D inhibitor) are under investigation in clinical trials and represent the most promising therapeutic approach. Plasma infusion may provide functional complement regulators in patients with genetic factor H deficiency. Treatment of C3NeF with rituximab or other B-cell depleting agents has been attempted with variable results. Corticosteroids and cyclophosphamide have limited efficacy. | Poor - DDD has a poor prognosis, with approximately 50% of patients progressing to ESRD within 10 years of diagnosis. Children tend to have more aggressive disease than adults. Post-transplant recurrence is nearly universal (>90% histologic recurrence), with graft loss from recurrence occurring in 40-50% within 10 years, making DDD one of the highest-risk recurrent diseases in transplantation. Retinal drusen may progress and cause visual impairment independent of renal disease. Acquired partial lipodystrophy does not reverse with renal disease treatment. Novel complement-targeted therapies offer hope for improved outcomes but long-term data are lacking. Factors associated with worse renal prognosis include crescentic histology, nephrotic-range proteinuria, elevated creatinine at diagnosis, and persistent low C3. | N05.8 |
| 8 | 7 | Fibrillary Glomerulonephritis | Glomerular Diseases | Fibrillary glomerulonephritis (FGN) is a rare glomerular disease characterized by the deposition of randomly arranged, non-branching fibrils (typically 16-24 nm in diameter) composed predominantly of DNAJB9 (DnaJ heat shock protein family member B9) within the glomerular mesangium and capillary walls. The fibrils are larger than amyloid fibrils (8-12 nm) and do not stain with Congo red, distinguishing FGN from renal amyloidosis. DNAJB9 was identified in 2018 as a highly sensitive and specific marker for FGN. The pathogenesis is not fully understood but appears to involve aberrant DNAJB9 secretion and polymerization, possibly triggered by immune dysregulation. Immunofluorescence typically shows polyclonal IgG deposition (predominantly IgG4 subclass), C3, and kappa and lambda light chains, suggesting a polyclonal immune process. FGN may rarely be associated with monoclonal immunoglobulin deposition. The light microscopy pattern is variable and includes MPGN pattern (most common), mesangial proliferative, diffuse proliferative, or membranous patterns. FGN may be associated with malignancy (10-15%), autoimmune disease, hepatitis C infection, or monoclonal gammopathy, though many cases are idiopathic. | FGN is a rare disease accounting for approximately 0.5-1% of native kidney biopsies. The estimated incidence is less than 1 per million per year. It is found predominantly in Caucasian patients. There is a slight female predominance (1.5:1). The mean age at diagnosis is approximately 50-60 years. FGN is associated with underlying malignancy in 10-15% of cases (most commonly carcinoma or lymphoma), autoimmune disease in 10-15%, and hepatitis C in 5-10%. | FGN predominantly presents in middle-aged to older adults, with a mean age at diagnosis of 50-60 years (range 20-80 years). It is very rare in children. The peak incidence is in the sixth decade. Elderly patients should be screened for associated malignancy, as the association increases with age. | Proteinuria is present in virtually all patients, with nephrotic-range proteinuria in 50-60% and full nephrotic syndrome in 40-50%. Microscopic hematuria is found in 60-70% of patients. Renal insufficiency (elevated serum creatinine) is present at diagnosis in 50-70%. Hypertension is common, present in 50-70%. The presentation may mimic many other glomerular diseases, and the diagnosis is typically made only after renal biopsy. Systemic symptoms related to associated diseases (malignancy, autoimmune disease, hepatitis C) may be present. There is no specific clinical feature that distinguishes FGN from other glomerulonephritides without biopsy. | Kidneys (glomeruli - mesangium and capillary walls); associated organs depending on underlying disease (malignancy, autoimmune conditions) | Renal biopsy is the only means of diagnosis. Light microscopy shows variable patterns (MPGN, mesangial proliferative, membranous, or diffuse proliferative). Immunofluorescence shows smudgy IgG and C3 deposition along capillary walls and mesangium. DNAJB9 immunohistochemistry staining on biopsy tissue is highly sensitive (98%) and specific (99%) for FGN and has become the diagnostic gold standard, often replacing the need for electron microscopy. Electron microscopy demonstrates randomly arranged, non-branching fibrils 16-24 nm in diameter within the mesangium and glomerular capillary walls. Congo red staining is negative, excluding amyloidosis. Serum and urine protein electrophoresis/immunofixation should be performed to exclude monoclonal gammopathy. Age-appropriate malignancy screening is recommended. Hepatitis B and C serologies, ANA, complement levels, and cryoglobulins should be checked. | There is no established standard therapy for FGN. Treatment with rituximab (375 mg/m2 weekly x 4 or 1 g IV x 2) has shown the most promise in recent retrospective studies, with partial or complete remission in 40-60% of patients, and is increasingly considered first-line immunosuppressive therapy. Corticosteroids alone have limited efficacy. Cyclophosphamide-based regimens have been used with variable success. Mycophenolate mofetil (1-2 g/day) has been tried but with inconsistent results. Supportive therapy with ACE inhibitors or ARBs for proteinuria and blood pressure control is essential. Treatment of any associated underlying condition (malignancy, hepatitis C, monoclonal gammopathy) may improve the renal disease. SGLT2 inhibitors may provide additional renoprotection. Given the rarity of FGN, treatment decisions are often individualized based on disease severity and associated conditions. | Poor - FGN has a generally poor prognosis, with approximately 40-50% of patients progressing to ESRD within 2-6 years of diagnosis. The median time from diagnosis to ESRD is approximately 4 years. Factors associated with worse prognosis include higher creatinine at diagnosis, nephrotic-range proteinuria, crescentic histology, and interstitial fibrosis on biopsy. Rituximab treatment may improve outcomes in patients who achieve remission. Post-transplant recurrence occurs in approximately 30-50% of patients, often within the first 2 years, and may lead to graft loss. Overall survival is affected by associated malignancies when present. With increasing recognition and earlier diagnosis facilitated by DNAJB9 staining, and emerging rituximab-based treatment, outcomes may improve. | N05.8 |
| 9 | 8 | Focal Segmental Glomerulosclerosis (FSGS) | Glomerular Diseases | FSGS is a pattern of glomerular injury characterized by segmental sclerosis affecting some (focal) but not all glomeruli, with multiple etiologic categories. Primary (idiopathic) FSGS is thought to involve a circulating permeability factor (likely soluble urokinase-type plasminogen activator receptor, suPAR, or cardiotrophin-like cytokine factor 1) that injures podocytes, causing foot process effacement, podocyte detachment from the GBM, and segmental sclerosis. Secondary FSGS results from adaptive responses to reduced nephron mass (obesity, unilateral nephrectomy, reflux nephropathy), hyperfiltration states, viral infections (HIV-associated nephropathy, parvovirus B19), drugs (heroin, pamidronate, lithium, interferon), or genetic mutations. Genetic FSGS involves mutations in over 60 podocyte-related genes including NPHS2 (podocin), ACTN4 (alpha-actinin-4), TRPC6, INF2, and APOL1 (apolipoprotein L1). APOL1 risk variants (G1 and G2) are found in 12-13% of African Americans and confer a 4-17 fold increased risk of FSGS and other kidney diseases. Histologic variants of FSGS include not-otherwise-specified (NOS), perihilar, cellular, tip lesion, and collapsing variants, each with distinct clinicopathologic features and prognoses. | FSGS is the most common primary glomerular disease in the United States and the leading cause of nephrotic syndrome in African Americans. It accounts for 20-25% of adult nephrotic syndrome and 35-40% of primary glomerular disease in adults. The incidence has been increasing over the past decades, currently estimated at 1.4-2.0 per 100,000 per year. FSGS is disproportionately common in African Americans (4-5 fold higher incidence than Caucasians), driven in part by APOL1 risk variants. Males are affected more often than females (1.5-2:1). FSGS accounts for approximately 4% of ESRD in the US and is the most rapidly growing cause of ESRD from primary glomerulonephritis. | Primary FSGS can occur at any age but has a peak incidence in adulthood (age 25-45 years). In children, FSGS accounts for 10-20% of idiopathic nephrotic syndrome and is more common in African American children. Genetic forms of FSGS may present in childhood (NPHS2 mutations) or young adulthood (ACTN4, TRPC6, INF2 mutations). APOL1-associated FSGS typically presents in young adulthood (ages 20-40) in African Americans. Secondary adaptive FSGS from obesity or reduced nephron mass may present at any age. | Nephrotic syndrome with heavy proteinuria (often >5-10 g/day) is the classic presentation of primary FSGS, with edema (peripheral and periorbital), hypoalbuminemia, and hyperlipidemia. Microscopic hematuria is present in 25-50% of patients but gross hematuria is uncommon. Hypertension is found in 30-50% at presentation and is more common than in minimal change disease. Renal insufficiency is present in 20-30% at diagnosis and is more common than in MCD. Secondary adaptive FSGS typically presents with non-nephrotic proteinuria (1-3 g/day) without full nephrotic syndrome. APOL1-associated FSGS may present with aggressive nephrotic syndrome and rapid progression. Collapsing FSGS (especially HIV-associated) presents with severe nephrotic syndrome, marked proteinuria, and rapidly declining renal function. Thromboembolic complications may occur as in any nephrotic syndrome, though less frequently than in membranous nephropathy. | Kidneys (glomeruli - podocytes and segmental sclerosis); cardiovascular system (hypertension, accelerated atherosclerosis); venous system (thromboembolic risk) | Renal biopsy is required for definitive diagnosis. Light microscopy shows segmental sclerosis (consolidation of the glomerular tuft with obliteration of capillary lumina) affecting some but not all glomeruli; the Columbia classification identifies five histologic variants. Immunofluorescence typically shows segmental IgM and C3 trapping in sclerotic areas (non-specific). Electron microscopy demonstrates diffuse podocyte foot process effacement in primary FSGS (typically >80%) versus segmental effacement in secondary FSGS (typically <50%). Urinalysis shows proteinuria (nephrotic range in primary FSGS), sometimes with microscopic hematuria. Serum albumin is low in nephrotic cases. APOL1 genotyping should be considered in patients of African ancestry. Secondary causes must be excluded: HIV testing, medication review, assessment for obesity-related or adaptive FSGS, and genetic testing in familial cases or steroid-resistant nephrotic syndrome. Serum suPAR levels are investigational. | Primary FSGS treatment begins with immunosuppressive therapy. High-dose corticosteroids (prednisone 1 mg/kg/day, maximum 80 mg/day, for a minimum of 4 weeks, up to 16 weeks if tolerated) are first-line, with a complete or partial remission rate of 40-60%. Calcineurin inhibitors (tacrolimus 0.05-0.1 mg/kg/day or cyclosporine 3-5 mg/kg/day) are used for steroid-resistant or steroid-dependent FSGS, achieving remission in 50-70%. Mycophenolate mofetil (1-2 g/day) combined with dexamethasone is an alternative for steroid-intolerant patients. Rituximab has shown benefit in steroid-dependent and frequently relapsing FSGS. Secondary and adaptive FSGS should be treated with supportive measures only: ACE inhibitors or ARBs for proteinuria reduction, weight loss for obesity-related FSGS, and treatment of the underlying cause. SGLT2 inhibitors (dapagliflozin 10 mg daily) provide additional antiproteinuric benefit. Genetic FSGS is generally steroid-resistant and managed supportively. Recurrence in transplanted kidneys occurs in 30-50% of primary FSGS cases (often within hours to days), sometimes requiring plasmapheresis. | Poor - Primary FSGS has a variable prognosis dependent on treatment response. Patients achieving complete remission (proteinuria <0.3 g/day) have excellent long-term outcomes with <5% ESRD risk at 10 years. Those achieving partial remission (proteinuria reduction >50% to <3.5 g/day) have a 15-25% ESRD risk at 10 years. Steroid-resistant FSGS carries a poor prognosis with 50-70% progressing to ESRD within 5-10 years. Collapsing FSGS has the worst prognosis among variants, with >50% reaching ESRD within 3 years. The tip lesion variant has the best prognosis, similar to minimal change disease. APOL1-associated FSGS tends to have a more aggressive course. Post-transplant recurrence (30-50% in primary FSGS) is a major concern, with graft loss from recurrence in 40-60% of those who recur. Overall, FSGS accounts for an increasing proportion of ESRD in the US. | N04.1 |
| 10 | 9 | IgA Nephropathy (Berger's Disease) | Glomerular Diseases | IgA nephropathy is the most common primary glomerulonephritis worldwide, characterized by predominant mesangial deposition of polymeric IgA1 with galactose-deficient hinge region O-glycans (Gd-IgA1). The pathogenesis follows a multi-hit model: Hit 1 involves increased circulating levels of Gd-IgA1 produced by mucosal B cells, particularly in the tonsils and gut-associated lymphoid tissue. Hit 2 involves the production of IgG and IgA autoantibodies directed against the galactose-deficient hinge region of Gd-IgA1. Hit 3 involves the formation of circulating immune complexes containing Gd-IgA1 and anti-glycan antibodies. Hit 4 involves mesangial deposition of these immune complexes, activating mesangial cells through IgA receptors (CD89, transferrin receptor), stimulating mesangial proliferation, extracellular matrix expansion, and complement activation via the alternative and lectin pathways. Activated mesangial cells release cytokines including TNF-alpha, IL-6, TGF-beta, and PDGF that drive glomerular inflammation and interstitial fibrosis. Genome-wide association studies have identified susceptibility loci in the MHC region (HLA-DQB1), complement factor H (CFH), DEFA gene cluster (encoding alpha-defensins), and genes involved in mucosal immune regulation. Mucosal infections, particularly upper respiratory tract infections, trigger synpharyngitic hematuria episodes through activation of mucosal IgA production. | IgA nephropathy is the most common primary glomerulonephritis worldwide, though its prevalence varies significantly by geography and ethnicity. It accounts for 30-40% of primary glomerulonephritis in East Asia (Japan, China, Korea), 20-25% in Europe, and 10-15% in North America. The incidence is estimated at 2.5 per 100,000 per year globally. The condition is 2-3 times more common in males than females in most populations. Prevalence is likely underestimated because diagnosis requires renal biopsy, and many patients with isolated microscopic hematuria are never biopsied. IgA nephropathy accounts for approximately 5-10% of ESRD in many countries. | IgA nephropathy can occur at any age but most commonly presents in the second to third decade of life, with peak incidence between ages 15 and 35 years. It is uncommon in children under age 5 and in adults over age 60, though it has been reported across all age groups. Males present at a younger age and with more aggressive disease than females. In children, the condition may present similarly to Henoch-Schonlein purpura (IgA vasculitis), which shares the same IgA1-mediated pathogenesis. | The classic presentation is episodic gross (macroscopic) hematuria occurring within 1-2 days of an upper respiratory tract infection (synpharyngitic hematuria), distinguishing it from post-streptococcal GN which typically occurs 1-3 weeks after infection. Persistent microscopic hematuria with or without mild proteinuria is the most common presentation, found in 30-40% of patients. Nephrotic-range proteinuria (>3.5 g/day) occurs in 5-10% of patients and indicates more severe disease. Hypertension is present in 20-30% at diagnosis and increases with disease duration. Acute kidney injury during episodes of gross hematuria may occur due to tubular obstruction by red cell casts. Flank pain during hematuria episodes is reported by some patients. A minority of patients (5-10%) present with rapidly progressive glomerulonephritis with crescent formation requiring urgent immunosuppressive therapy. | Kidneys (glomerular mesangium); tonsils and gut-associated lymphoid tissue (source of Gd-IgA1); skin, joints, GI tract (in IgA vasculitis/Henoch-Schonlein purpura overlap) | Definitive diagnosis requires renal biopsy showing predominant or co-dominant mesangial IgA deposition on immunofluorescence microscopy, which is the gold standard finding. Light microscopy typically shows mesangial hypercellularity and matrix expansion (Oxford MEST-C classification scores: M for mesangial hypercellularity, E for endocapillary proliferation, S for segmental sclerosis, T for tubular atrophy/interstitial fibrosis, C for crescents). Electron microscopy demonstrates electron-dense mesangial deposits. Serum IgA levels are elevated in 30-50% of patients but are not specific. Urinalysis shows persistent microscopic hematuria with dysmorphic red blood cells and red blood cell casts. Proteinuria quantification (24-hour urine or spot urine protein-to-creatinine ratio) is essential for risk stratification. The International IgA Nephropathy Prediction Tool incorporates eGFR, proteinuria, blood pressure, MEST-C scores, age, and race to predict 5-year risk of ESRD. | Supportive therapy with maximally tolerated RAS blockade is the cornerstone: ACE inhibitors (ramipril 2.5-10 mg daily) or ARBs (losartan 50-100 mg daily, valsartan 80-320 mg daily) titrated to achieve proteinuria below 0.5-1.0 g/day, with blood pressure target below 125/75 mmHg per KDIGO 2021 guidelines. SGLT2 inhibitors (dapagliflozin 10 mg daily) provide additional antiproteinuric and renoprotective benefit based on DAPA-CKD trial data. Targeted-release budesonide (Nefecon/Tarpeyo 16 mg daily for 9 months) is FDA-approved specifically for IgA nephropathy with proteinuria >1 g/day despite optimized supportive care, targeting mucosal B cells in the ileum. Systemic corticosteroids (methylprednisolone pulse followed by oral prednisolone 0.5-1 mg/kg/day tapered over 6 months) may be considered for high-risk patients based on the TESTING trial (with reduced-dose protocol to minimize toxicity). Mycophenolate mofetil (1-2 g/day) shows benefit primarily in Asian populations. Fish oil (omega-3 fatty acids, 3-4 g/day) has modest antiproteinuric effects. Tonsillectomy combined with steroid pulse therapy is practiced in Japan with favorable outcomes in selected patients. | Variable - Variable prognosis; approximately 20-40% of patients progress to ESRD over 20-30 years. The rate of GFR decline averages 1-3 mL/min/year in progressive disease. Key adverse prognostic factors include persistent proteinuria above 1 g/day, hypertension, reduced eGFR at presentation, MEST-C scores showing tubular atrophy/interstitial fibrosis (T1-T2) and crescents (C1-C2), and male sex. Patients achieving sustained proteinuria below 0.5 g/day have excellent long-term prognosis with less than 5% risk of ESRD. Approximately 15-20% of patients have a benign course with stable microscopic hematuria and minimal proteinuria. IgA nephropathy recurs in kidney transplants in 30-60% histologically, though clinically significant recurrence causing graft loss occurs in only 5-10% by 10 years. | N02.8 |
| 11 | 10 | Immunotactoid Glomerulopathy | Glomerular Diseases | Immunotactoid glomerulopathy (ITG) is an extremely rare glomerular disease characterized by organized microtubular deposits (typically 30-50 nm in diameter) with a hollow core arranged in parallel arrays within the glomerular mesangium and capillary walls. Unlike fibrillary GN, the microtubular deposits in ITG are larger, hollow, and arranged in organized parallel bundles rather than randomly. ITG is strongly associated with lymphoproliferative disorders and monoclonal gammopathy: approximately 50-70% of patients have an identifiable monoclonal protein (most commonly IgG kappa), and 30-50% have an underlying B-cell lymphoproliferative disorder (chronic lymphocytic leukemia, lymphoma, Waldenstrom's macroglobulinemia). The organized deposits likely result from precipitation and crystallization of monoclonal immunoglobulin at the glomerular filtration barrier. Immunofluorescence typically shows IgG and C3 deposition, often with light chain restriction (monoclonal). The light microscopy pattern is most commonly MPGN or membranous, though other patterns may be seen. ITG is distinguished from FGN by the larger diameter and parallel arrangement of microtubules, and from amyloidosis by the absence of Congo red staining and the microtubular (rather than fibrillar) ultrastructure. | ITG is exceedingly rare, accounting for approximately 0.06-0.1% of native kidney biopsies. Due to its rarity, precise incidence and prevalence estimates are difficult to establish. Only several hundred cases have been reported in the literature. There is a slight male predominance. The mean age at diagnosis is 55-65 years, reflecting the association with lymphoproliferative disorders and monoclonal gammopathy, which are more common in older adults. | ITG predominantly presents in middle-aged to elderly adults, with a mean age at diagnosis of 55-65 years. It is extremely rare in children and young adults. Given the strong association with lymphoproliferative disorders, the age distribution parallels that of hematologic malignancies. | Nephrotic syndrome is the most common presentation, occurring in 50-70% of patients, with heavy proteinuria, peripheral edema, hypoalbuminemia, and hyperlipidemia. Renal insufficiency is present at diagnosis in 40-60% of patients. Microscopic hematuria is found in 60-80%. Hypertension is present in 40-60%. Symptoms related to the underlying lymphoproliferative disorder (lymphadenopathy, splenomegaly, constitutional symptoms, cytopenias) may be present. The clinical presentation is non-specific and indistinguishable from other forms of glomerulonephritis without biopsy. | Kidneys (glomeruli - mesangium and capillary walls); bone marrow (in associated lymphoproliferative disorders); lymph nodes and spleen (in associated lymphoma); blood (monoclonal gammopathy) | Renal biopsy is the only means of diagnosis. Light microscopy shows variable patterns, most commonly MPGN or membranous. Immunofluorescence shows IgG and C3 deposition, often with monoclonal light chain restriction (kappa > lambda). DNAJB9 staining is negative, distinguishing from FGN. Electron microscopy is diagnostic, showing microtubular deposits 30-50 nm in diameter with a hollow core arranged in organized parallel arrays. Congo red is negative, excluding amyloidosis. Comprehensive evaluation for underlying monoclonal gammopathy and lymphoproliferative disease is essential: serum and urine protein electrophoresis with immunofixation, serum free light chains, bone marrow biopsy, CT scan of chest/abdomen/pelvis, and flow cytometry of peripheral blood. | Treatment is directed at the underlying hematologic disorder when present. For ITG associated with B-cell lymphoproliferative disorders: rituximab-based chemotherapy (R-CVP, R-CHOP, or bendamustine-rituximab depending on the specific diagnosis) targeting the underlying clone. For ITG associated with monoclonal gammopathy of renal significance (MGRS): clone-directed therapy with rituximab (if B-cell clone) or bortezomib-based regimens (if plasma cell clone). For idiopathic ITG without identifiable monoclonal protein: rituximab (375 mg/m2 weekly x 4), corticosteroids, or cyclophosphamide-based regimens have been tried with variable success. Supportive care with ACE inhibitors or ARBs, diuretics for edema, and statin therapy for hyperlipidemia. Given the rarity of the disease, treatment is largely based on case reports and expert opinion. | Poor - ITG has a poor prognosis overall, with approximately 40-60% of patients progressing to ESRD within 5 years. Patients who respond to treatment of the underlying hematologic disorder generally have better renal outcomes, with some achieving partial or complete remission of proteinuria. Those with idiopathic ITG have a more variable prognosis. The 5-year patient survival is approximately 60-70%, influenced by the presence and severity of underlying malignancy. Post-transplant recurrence has been reported but the exact rate is uncertain due to the rarity of the disease. Early identification and treatment of associated lymphoproliferative disorders may improve outcomes. | N05.8 |
| 12 | 11 | Lupus Nephritis | Glomerular Diseases | Lupus nephritis (LN) is one of the most serious manifestations of systemic lupus erythematosus (SLE), occurring when autoantibodies (particularly anti-dsDNA antibodies) form immune complexes that deposit in glomeruli, activating complement and triggering an inflammatory cascade. The pathogenesis involves loss of immune tolerance to nuclear antigens, production of pathogenic autoantibodies (anti-dsDNA, anti-nucleosome, anti-C1q, anti-Smith), formation of circulating immune complexes and in situ immune complex formation through binding of anti-dsDNA antibodies to nucleosomes planted in the GBM, and complement activation via classical pathway (C1q, C4, C3, C5b-9). The ISN/RPS 2003 (revised 2018) classification divides LN into six classes: Class I (minimal mesangial), Class II (mesangial proliferative), Class III (focal proliferative, <50% glomeruli), Class IV (diffuse proliferative, ≥50% glomeruli), Class V (membranous), and Class VI (advanced sclerotic, >90% globally sclerosed glomeruli). Classes III and IV are the most common and clinically significant, often presenting with active nephritis. Transformation between classes occurs during the disease course. Full-house immunofluorescence (IgG, IgA, IgM, C3, C1q deposition) is characteristic and nearly pathognomonic of lupus nephritis. | Lupus nephritis occurs in approximately 35-60% of SLE patients, with higher rates in certain ethnic groups. The prevalence is significantly higher in African Americans (50-70%), Hispanics (40-60%), and Asians (40-60%) compared to Caucasians (20-30%). Among SLE patients, LN is the strongest predictor of morbidity and mortality. SLE predominantly affects females (9:1 female-to-male ratio), and lupus nephritis follows the same pattern. The incidence of SLE varies globally: approximately 5 per 100,000 in the US, with 3-4 fold higher rates in African Americans. LN accounts for approximately 1-2% of all ESRD. | Lupus nephritis typically develops within the first 5 years of SLE diagnosis, with the highest risk in the first 2-3 years. Peak incidence corresponds to the peak age of SLE onset: 15-45 years in women. Childhood-onset SLE (before age 18) has a higher rate of renal involvement (60-80%) compared to adult-onset SLE (35-55%). Male SLE patients have a higher frequency and more severe lupus nephritis than females. Late-onset SLE (after age 50) may also develop LN but tends to have a more indolent course. | Active lupus nephritis may present with a wide spectrum from asymptomatic urinary abnormalities to rapidly progressive glomerulonephritis. Proteinuria is the most common finding, present in >90% of LN patients; nephrotic-range proteinuria (>3.5 g/day) occurs in 40-65% of Class V and many Class IV patients. Microscopic hematuria with dysmorphic RBCs and RBC casts is present in 60-80% of active proliferative LN. Hypertension develops in 30-50% of patients. Renal insufficiency (elevated creatinine) is present at diagnosis in 20-30% of proliferative LN patients. Peripheral edema, ascites, and pleural effusions occur in nephrotic patients. Systemic SLE manifestations including malar rash, arthralgias, oral ulcers, serositis, and fatigue often accompany renal involvement. Acute kidney injury may develop rapidly in severe Class IV LN with active crescents. Hypocomplementemia (low C3 and C4) and elevated anti-dsDNA titers are found in active LN and serve as disease activity markers. | Kidneys (glomeruli, tubulointerstitium, renal vasculature); skin; joints; serous membranes (pleura, pericardium); hematologic system; central nervous system; vascular endothelium | Renal biopsy is essential for classification and guiding treatment. Light microscopy identifies the ISN/RPS class and evaluates activity (cellularity, necrosis, crescents) and chronicity (sclerosis, fibrosis) indices. Immunofluorescence typically shows 'full-house' staining with IgG, IgA, IgM, C3, and C1q, which is highly characteristic of LN. Electron microscopy demonstrates immune deposits in mesangial, subendothelial, and/or subepithelial locations depending on the class. Anti-dsDNA antibody titers correlate with disease activity and should be monitored serially. Complement levels (C3, C4, CH50) are typically low during active LN and normalize with treatment response. Complete urinalysis with microscopy, spot urine protein-to-creatinine ratio, and 24-hour urine protein should be monitored regularly. Serum creatinine and eGFR track renal function. Anti-C1q antibodies may be a more specific marker of renal involvement. Repeat biopsy should be considered for flares or inadequate treatment response. | Treatment is guided by histologic class and activity. Class I/II: supportive care with ACE inhibitors/ARBs and hydroxychloroquine (200-400 mg/day, a cornerstone of all LN treatment). Class III/IV (active proliferative LN): induction with mycophenolate mofetil (2-3 g/day for 6 months, preferred in most patients, especially African Americans and Hispanics based on ALMS trial) or IV cyclophosphamide (Euro-Lupus low-dose protocol: 500 mg IV every 2 weeks x 6 doses, or NIH protocol: 0.5-1 g/m2 monthly x 6 months), combined with corticosteroids (IV methylprednisolone 500-1000 mg x 3 days followed by oral prednisone 0.5-1 mg/kg/day tapered to ≤7.5 mg/day by 3-6 months). Voclosporin (23.7 mg twice daily), a novel calcineurin inhibitor, received FDA approval in 2021 for active LN when added to mycophenolate and low-dose steroids, based on the AURORA trial showing significantly higher complete response rates. Belimumab (10 mg/kg IV monthly or 200 mg SC weekly), an anti-BAFF antibody, is also FDA-approved as add-on therapy for active LN. Maintenance therapy with mycophenolate (1-2 g/day) or azathioprine (2 mg/kg/day) for at least 3-5 years. Class V: rituximab (1 g x 2) or calcineurin inhibitors may be added for persistent nephrotic syndrome. Hydroxychloroquine should be continued lifelong as it reduces flare rates and mortality. | Variable - With modern immunosuppressive therapy, the 10-year renal survival for proliferative LN (Class III/IV) has improved to 80-90% in most studies, up from 50% in the pre-immunosuppressive era. Complete renal response (proteinuria <0.5 g/day, normal creatinine, inactive sediment) at 12 months is the strongest predictor of favorable long-term outcome and is achieved in 30-50% with standard induction. Renal flares occur in 25-50% of patients during maintenance therapy and require intensification of treatment. African Americans and Hispanics have worse renal outcomes compared to Caucasians and Asians. Lupus nephritis accounts for 1-2% of ESRD; once on dialysis, SLE paradoxically becomes clinically quiescent. Kidney transplant outcomes in LN patients are generally good, with recurrence occurring in approximately 5-10% of allografts. Overall mortality in LN has decreased significantly but remains 2-3 fold higher than in SLE without renal involvement. | M32.14 |
| 13 | 12 | Membranoproliferative Glomerulonephritis (MPGN) | Glomerular Diseases | MPGN is a pattern of glomerular injury characterized by mesangial proliferation, endocapillary proliferation, capillary wall remodeling with GBM duplication (double contours or 'tram-tracking'), and lobular accentuation of the glomerular tuft. The modern classification divides MPGN by pathogenesis rather than electron microscopic deposit pattern: immune complex-mediated MPGN (most common) results from chronic immune complex deposition driven by chronic infections (hepatitis C in 60-70% of cases, hepatitis B, endocarditis, shunt nephritis), autoimmune diseases (SLE, cryoglobulinemia, Sjogren's), or monoclonal gammopathy (MGRS). Complement-mediated MPGN results from dysregulation of the alternative complement pathway due to acquired autoantibodies (C3 nephritic factor, anti-factor H antibodies) or genetic mutations in complement regulatory genes (CFH, CFI, CFB, C3, MCP), leading to uncontrolled C3 activation and deposition (C3 glomerulopathy). The hallmark double contour formation results from mesangial cell interposition between the endothelial cell and the GBM, with new basement membrane material laid down on either side of the interposed cells. Endocapillary proliferation and monocyte infiltration contribute to capillary wall thickening and luminal narrowing. | MPGN is relatively uncommon in developed countries, accounting for approximately 5-10% of primary glomerulonephritis in adults and 5-7% in children in biopsy series. The incidence has declined significantly in developed nations due to reduced prevalence of chronic infections (hepatitis B vaccination, hepatitis C treatment). In developing countries where hepatitis B and C remain prevalent, MPGN accounts for a higher proportion of glomerulonephritis. C3 glomerulopathy is very rare, with an estimated incidence of 1-2 per million per year. MPGN associated with monoclonal gammopathy (MGRS) is increasingly recognized in elderly populations. There is no significant gender predilection. | Immune complex-mediated MPGN associated with hepatitis C typically presents in adults aged 40-60 years. Childhood MPGN most commonly presents between ages 8 and 16 years and is more likely to be complement-mediated (C3 glomerulopathy). MPGN associated with monoclonal gammopathy tends to present in older adults (>50 years). C3 glomerulopathy can present at any age, from childhood to adulthood, depending on the underlying complement abnormality. | MPGN has a variable clinical presentation. Nephrotic syndrome (heavy proteinuria, edema, hypoalbuminemia) is the most common presentation, occurring in 40-50% of patients. Nephritic-nephrotic syndrome with hematuria, proteinuria, hypertension, and renal impairment occurs in 20-30%. Acute nephritic syndrome mimicking post-infectious GN occurs in some patients. Asymptomatic urinary abnormalities (proteinuria with microscopic hematuria) are found incidentally in 20-30%. Hypocomplementemia (low C3 with or without low C4) is a characteristic laboratory finding. Hypertension is present in 50-70% of patients at diagnosis. Microscopic hematuria is almost universal, and gross hematuria may occur. Serum creatinine is elevated in 30-50% at presentation. Cryoglobulinemia associated with hepatitis C may cause palpable purpura, arthralgias, peripheral neuropathy, and hepatic dysfunction. | Kidneys (glomeruli - mesangium, capillary walls, GBM); liver (in hepatitis-associated cases); skin, joints, peripheral nerves (in cryoglobulinemic MPGN); complement system (in C3 glomerulopathy) | Renal biopsy is essential for diagnosis. Light microscopy shows the characteristic pattern of mesangial and endocapillary proliferation with lobular accentuation and GBM double contours on silver or PAS staining. Immunofluorescence is critical for classification: dominant or codominant C3 with absent or scanty immunoglobulin staining suggests C3 glomerulopathy, while IgG, IgM, C3, and C1q staining suggests immune complex-mediated MPGN. Electron microscopy demonstrates subendothelial and mesangial deposits, with the pattern of deposits further aiding classification. Serum complement levels: low C3 with normal C4 suggests alternative pathway activation (C3 glomerulopathy), while low C3 and low C4 suggest classical pathway activation (immune complex-mediated). C3 nephritic factor (C3NeF) is positive in 50-80% of dense deposit disease and 40-50% of C3 glomerulonephritis. Hepatitis B and C serologies, cryoglobulins, serum and urine protein electrophoresis/immunofixation, and ANA/dsDNA should be checked. Genetic testing for complement regulatory gene mutations is recommended in C3 glomerulopathy. | Treatment depends on the underlying etiology. Hepatitis C-associated MPGN is treated with direct-acting antiviral therapy (e.g., sofosbuvir/velpatasvir for 12 weeks), which achieves viral eradication and often remission of glomerulonephritis. For cryoglobulinemic vasculitis with severe renal involvement, rituximab (375 mg/m2 weekly x 4) combined with corticosteroids is first-line. MGRS-associated MPGN is treated with clone-directed therapy targeting the underlying B-cell or plasma cell clone (e.g., bortezomib-based regimens or rituximab). C3 glomerulopathy has limited treatment options: mycophenolate mofetil (1-2 g/day) has shown benefit in some studies. Complement inhibitors (eculizumab 900 mg IV every 2 weeks, targeting C5) have shown variable results in C3 glomerulopathy but may benefit patients with active proliferative disease. Iptacopan (factor B inhibitor) is under investigation for C3 glomerulopathy. Supportive measures include ACE inhibitors or ARBs, blood pressure control, and statin therapy. Idiopathic immune complex MPGN in children may be treated with corticosteroids and antiplatelet agents. | Poor - MPGN generally has a progressive course, with approximately 40-60% of patients progressing to ESRD within 10 years without treatment. Hepatitis C-associated MPGN has significantly improved outcomes with direct-acting antiviral therapy, with renal remission achieved in 50-70% of patients. C3 glomerulopathy has a variable prognosis: dense deposit disease has a particularly poor prognosis with 50% reaching ESRD by 10 years, while C3 glomerulonephritis has a somewhat better prognosis. MPGN recurs in transplanted kidneys in 30-70% of cases (particularly C3 glomerulopathy, with up to 50-80% histologic recurrence), with graft loss from recurrence in 15-30%. Early identification and treatment of the underlying cause significantly improves outcomes. Children generally have better prognosis than adults with MPGN. | N05.5 |
| 14 | 13 | Membranous Nephropathy | Glomerular Diseases | Membranous nephropathy (MN) is an autoimmune glomerular disease characterized by subepithelial immune complex deposition along the glomerular basement membrane (GBM), leading to GBM thickening and nephrotic syndrome. Primary MN (approximately 75-80% of cases) is most commonly caused by circulating autoantibodies targeting the M-type phospholipase A2 receptor (PLA2R, present in 70-80% of primary MN) or thrombospondin type-1 domain-containing 7A (THSD7A, in 2-5%). PLA2R is a transmembrane glycoprotein expressed on podocyte foot processes, and anti-PLA2R IgG4 antibodies bind to it in situ, forming subepithelial immune deposits. These deposits activate the complement cascade via the membrane attack complex (C5b-9), which inserts into the podocyte membrane causing sublytic injury, cytoskeletal disruption, and alterations in slit diaphragm proteins, resulting in increased glomerular permeability to albumin. Secondary MN (20-25% of cases) is associated with systemic lupus erythematosus, hepatitis B or C infection, malignancy (solid tumors in 5-10%, especially lung, colon, breast), drugs (NSAIDs, gold, penicillamine), and sarcoidosis. Histologically, MN is characterized by diffuse GBM thickening with subepithelial deposits visible on silver staining as 'spikes' and on electron microscopy as electron-dense subepithelial deposits. | MN is the most common cause of nephrotic syndrome in non-diabetic white adults, accounting for 20-30% of adult nephrotic syndrome cases in Western countries. The incidence is approximately 1-1.2 per 100,000 per year, with a prevalence of approximately 10 per 100,000. Males are affected 2-3 times more often than females. The mean age at diagnosis is 50-60 years. In Asian populations, MN is the second most common cause of adult nephrotic syndrome after IgA nephropathy. Secondary MN associated with malignancy increases in frequency with advancing age, particularly in patients over 60 years. | Primary MN most commonly presents in adults aged 40-60 years, with a male predominance. It is uncommon in children, where secondary causes (particularly SLE and hepatitis B) should be strongly considered. In adults over 65 years, the association with underlying malignancy should be actively investigated. Secondary MN associated with lupus typically presents in younger adults and may present at any age depending on the underlying cause. | Nephrotic syndrome is the presenting feature in approximately 70-80% of patients, with insidious onset of peripheral edema (lower extremity and periorbital), foamy urine from heavy proteinuria, hypoalbuminemia (serum albumin often <2.5 g/dL), and hyperlipidemia. Non-nephrotic proteinuria (1-3.5 g/day) is the presenting feature in the remaining 20-30%. Thromboembolic complications are particularly common in MN compared to other nephrotic syndromes, affecting 20-30% of patients, with renal vein thrombosis (in up to 35%) and pulmonary embolism being the most serious. Microscopic hematuria is present in 30-50% but gross hematuria is rare. Hypertension develops in 20-50% of patients during the disease course. Renal function is typically preserved at presentation, with elevated creatinine found in only 10-20%. Fatigue, malaise, and loss of appetite accompany the nephrotic state. | Kidneys (glomerular basement membrane, podocytes); venous system (thromboembolic complications); cardiovascular system (accelerated atherosclerosis from hyperlipidemia) | Renal biopsy is essential for diagnosis. Light microscopy shows diffuse thickening of the GBM without significant hypercellularity. Silver staining (Jones methenamine silver) demonstrates subepithelial 'spikes' projecting from the GBM. Immunofluorescence shows granular IgG4 (predominant subclass in primary MN) and C3 deposition along the capillary walls. Electron microscopy demonstrates subepithelial electron-dense deposits with varying stages of GBM reaction (Ehrenreich-Churg stages I-IV). Anti-PLA2R antibody testing (serum ELISA or immunofluorescence) is positive in 70-80% of primary MN and is highly specific; titers correlate with disease activity and response to treatment. Anti-THSD7A antibodies should be tested if PLA2R is negative. PLA2R staining on biopsy tissue by immunohistochemistry is more sensitive than serum testing. Secondary causes must be excluded: antinuclear antibodies, hepatitis B and C serologies, complement levels (C3, C4), and age-appropriate cancer screening (CT chest/abdomen/pelvis, colonoscopy). | Supportive care for all patients includes ACE inhibitors or ARBs for antiproteinuric effect and blood pressure control, dietary sodium restriction (<2 g/day), diuretics for edema management, and statin therapy for hyperlipidemia. Anticoagulation with warfarin (INR 2-3) or direct oral anticoagulants is recommended when serum albumin falls below 2.0-2.5 g/dL due to high thrombotic risk. Immunosuppressive therapy is indicated for patients at moderate-to-high risk of progression (persistent nephrotic-range proteinuria despite 6 months of supportive care, rising creatinine, or severe nephrotic complications). First-line immunosuppressive options include rituximab (1 g IV on days 1 and 15, or 375 mg/m2 weekly x 4), which has become the preferred agent based on the MENTOR and STARMEN trials. Cyclophosphamide-based regimens (modified Ponticelli protocol: alternating months of IV methylprednisolone 1 g x 3 days followed by oral prednisone, and oral cyclophosphamide 2-2.5 mg/kg/day for 6 months) remain effective alternatives. Calcineurin inhibitors (tacrolimus 0.05-0.075 mg/kg/day or cyclosporine 3.5-5 mg/kg/day) achieve remission in 70-80% but have high relapse rates upon discontinuation. Anti-PLA2R antibody levels guide treatment response monitoring. | Variable - Spontaneous complete or partial remission occurs in approximately 30-40% of patients within 12-24 months without immunosuppressive therapy. With rituximab treatment, complete or partial remission is achieved in 60-80% of patients by 24 months. Approximately 30-40% of untreated nephrotic patients progress to CKD or ESRD over 10-15 years. Anti-PLA2R antibody decline or disappearance (immunologic remission) precedes proteinuria reduction by 3-6 months and predicts favorable outcome. Five-year renal survival exceeds 90% with appropriate treatment. Recurrence after kidney transplantation occurs in 30-40% of patients, particularly those with persistent anti-PLA2R antibodies, though graft loss from recurrence is uncommon (5-10%). Membranous nephropathy associated with malignancy may resolve with successful cancer treatment. | N04.2 |
| 15 | 14 | Minimal Change Disease | Glomerular Diseases | Minimal change disease (MCD) is the most common cause of nephrotic syndrome in children, characterized by diffuse podocyte foot process effacement on electron microscopy with no significant abnormalities on light microscopy or immunofluorescence. The pathogenesis remains incompletely understood but is believed to involve T-cell dysregulation with production of circulating factors (possibly c-maf inducing protein, or angiopoietin-like 4) that alter podocyte function and increase glomerular permeability. Evidence for immune dysregulation includes the frequent association with allergic conditions (atopy, asthma, eczema), remission with viral infections such as measles (which suppress T-cell function), response to corticosteroids and calcineurin inhibitors, and association with Hodgkin lymphoma. Recent evidence also suggests B-cell involvement, supported by the efficacy of rituximab in relapsing disease. The podocyte injury leads to reorganization of the actin cytoskeleton, loss of slit diaphragm integrity, and charge barrier disruption (loss of podocalyxin and heparan sulfate proteoglycans), resulting in selective proteinuria (predominantly albuminuria) in most cases. MCD may rarely be secondary to drugs (NSAIDs, lithium, interferon), infections, or malignancy (Hodgkin lymphoma). | MCD accounts for 70-90% of idiopathic nephrotic syndrome in children under age 10 and approximately 10-25% in adults. The incidence in children is approximately 2-7 per 100,000 children per year, with a prevalence of approximately 16 per 100,000 children. In adults, MCD accounts for approximately 10-25% of nephrotic syndrome cases. The male-to-female ratio is approximately 2:1 in children but approximately 1:1 in adults. MCD is more common in South Asian and East Asian populations. There are no significant racial differences in incidence in the United States after adjusting for age. | MCD most commonly presents in children aged 2-6 years, with a peak incidence at age 3-4 years. In adults, MCD can present at any age but is most common in young adults (20-40 years). Elderly adults can also develop MCD, where it may be associated with NSAID use or lymphoproliferative disorders. Relapsing disease often continues throughout childhood and into adolescence, with the majority of children eventually outgrowing the tendency to relapse by late adolescence. | Abrupt onset of nephrotic syndrome is the classic presentation, with rapid development of periorbital edema (often noticed first upon waking), followed by lower extremity edema, genital edema, and ascites. Massive proteinuria (>40 mg/m2/hr in children or >3.5 g/day in adults) causes severe hypoalbuminemia (serum albumin often <2.0 g/dL). The urine may appear frothy or foamy. Weight gain from fluid retention can be dramatic (5-10 kg in children, more in adults). Hypertension is present in approximately 10-20% of children and 30-50% of adults. Microscopic hematuria is found in approximately 15-20% of cases but gross hematuria is very rare. Acute kidney injury may occur in severe cases from intravascular volume depletion or bilateral renal vein thrombosis. Peritonitis (especially Streptococcus pneumoniae in children) may complicate the nephrotic state due to urinary loss of opsonins and immunoglobulins. | Kidneys (glomerular podocytes - foot process effacement); immune system (T-cell and possibly B-cell dysregulation); serosal cavities (ascites, pleural effusions from nephrotic state) | In children aged 1-10 years with typical nephrotic syndrome, the diagnosis is presumed to be MCD and empiric corticosteroid therapy is initiated without renal biopsy, as MCD accounts for 70-90% of cases in this age group and >90% respond to steroids. Renal biopsy is indicated in steroid-resistant cases (no remission after 4-8 weeks of adequate steroid therapy), in adults, and in atypical presentations (persistent hematuria, low complement, renal insufficiency). Light microscopy is characteristically normal or shows only minor changes (mild mesangial hypercellularity). Immunofluorescence is typically negative or shows trace IgM in mesangium. Electron microscopy shows diffuse podocyte foot process effacement (>80%), which is the defining feature. Urinalysis shows massive proteinuria with oval fat bodies; selective proteinuria (albumin selectivity index >0.2) suggests MCD over FSGS. Serum complement levels (C3, C4) are normal, distinguishing MCD from complement-mediated glomerulonephritis. | Corticosteroids are first-line therapy. In children, prednisone 60 mg/m2/day (maximum 60 mg) for 4-6 weeks followed by 40 mg/m2 on alternate days for 4-6 weeks, with gradual taper; >90% of children achieve complete remission within 4 weeks. In adults, prednisone 1 mg/kg/day (maximum 80 mg) for a minimum of 4 weeks, extending to 16 weeks if necessary; remission rates are 75-85% but slower than in children. Frequently relapsing or steroid-dependent MCD requires steroid-sparing agents: cyclophosphamide (2 mg/kg/day for 8-12 weeks) achieves sustained remission in 60-70% of children. Calcineurin inhibitors (cyclosporine 3-5 mg/kg/day or tacrolimus 0.05-0.1 mg/kg/day) maintain remission in 80-90% but relapse is common upon withdrawal. Mycophenolate mofetil (1-2 g/day) is used for steroid-dependent cases as an alternative to calcineurin inhibitors. Rituximab (375 mg/m2 x 1-4 doses) has shown excellent efficacy in frequently relapsing/steroid-dependent MCD, maintaining remission in 60-80% at 1-2 years. Levamisole (2.5 mg/kg on alternate days) is used in some centers for relapsing MCD in children. | Good - Excellent long-term prognosis with appropriate treatment. In children, >95% respond to corticosteroids (steroid-sensitive), and long-term renal prognosis is excellent with <1% progressing to ESRD. However, 50-70% of children experience at least one relapse, and 30-50% become frequently relapsing or steroid-dependent, requiring steroid-sparing agents. Most children outgrow the disease by late adolescence/early adulthood. In adults, response to steroids is slower (median 3-4 weeks vs. 1-2 weeks in children) and relapse rates are approximately 50-70%. Adult MCD rarely progresses to ESRD (<5% over 10 years). The major morbidity is related to long-term steroid and immunosuppressive therapy side effects (obesity, growth retardation, osteoporosis, diabetes, infections). Overall life expectancy is normal in the vast majority of patients with MCD. | N04.0 |
| 16 | 15 | Post-Streptococcal Glomerulonephritis | Glomerular Diseases | Post-streptococcal glomerulonephritis (PSGN) is the prototypical post-infectious glomerulonephritis, caused by immune-mediated glomerular injury following infection with nephritogenic strains of group A beta-hemolytic streptococcus (Streptococcus pyogenes). Specific nephritogenic strains include M-types 1, 2, 4, 12, 25, and 49, with M-type 12 most commonly associated with pharyngeal infections and M-type 49 with skin infections (impetigo). Two streptococcal antigens have been identified as key pathogenic factors: nephritis-associated plasmin receptor (NAPlr/glyceraldehyde-3-phosphate dehydrogenase) and streptococcal pyrogenic exotoxin B (SPE B), both of which activate the alternative complement pathway and deposit in glomeruli. The pathogenesis involves immune complex formation (both circulating and in situ) with complement activation predominantly via the alternative pathway (resulting in characteristically low C3 with normal C4), neutrophil infiltration, mesangial cell proliferation, and endocapillary hypercellularity. The characteristic 'humps' seen on electron microscopy represent subepithelial immune deposits. The latency period between infection and nephritis (1-3 weeks after pharyngitis, 3-6 weeks after skin infection) reflects the time required for antibody production and immune complex formation. | PSGN is the most common form of acute glomerulonephritis worldwide, predominantly affecting children in developing countries. The global incidence is estimated at 472,000 new cases per year, with >97% occurring in developing nations. In developed countries, PSGN has declined dramatically due to improved hygiene and antibiotic treatment of streptococcal infections, with an incidence of approximately 0.3 per 100,000 per year. In developing countries, the incidence remains high at 9.5-28.5 per 100,000 per year. Males are affected approximately twice as often as females. Subclinical PSGN (asymptomatic microscopic hematuria and complement consumption detected only by screening during epidemics) is 4-10 times more common than clinical disease. | PSGN most commonly affects children aged 5-12 years, with a peak incidence at age 6-8 years. It is uncommon in children under age 3 years. In developing countries, skin infection-associated PSGN may occur in younger children (age 2-6). Adults may also develop PSGN, particularly elderly or immunocompromised individuals, in whom the prognosis is worse. Epidemic forms occur in communities with poor sanitation, while sporadic cases occur worldwide. | The classic presentation is acute nephritic syndrome with sudden onset of cola-colored or tea-colored urine (macroscopic hematuria from dysmorphic RBCs), facial and periorbital edema (most prominent in the morning), and oliguria, occurring 1-3 weeks after pharyngitis or 3-6 weeks after skin infection. Hypertension is present in 60-80% of children and may be severe enough to cause hypertensive encephalopathy (headache, seizures, visual disturbances). Edema is present in 65-90% and is caused by sodium and water retention rather than hypoalbuminemia. Proteinuria is usually non-nephrotic (<3.5 g/day) but nephrotic-range proteinuria occurs in 5-10% of cases. Oliguria (urine output <400 mL/day) develops in 10-50% of patients. Serum creatinine is mildly to moderately elevated in most patients. Pulmonary congestion and congestive heart failure may occur from volume overload, particularly in adults. Constitutional symptoms including malaise, headache, and abdominal pain are common. | Kidneys (glomeruli - endocapillary proliferation, subepithelial immune deposits); cardiovascular system (hypertension, volume overload); respiratory system (pulmonary edema from volume overload) | Diagnosis is primarily clinical based on the triad of hematuria, hypertension, and edema following a latent period after streptococcal infection. Evidence of recent streptococcal infection includes positive throat or skin culture (often negative by the time nephritis develops), elevated anti-streptolysin O (ASO) titer (>200 IU/mL, positive in 75% after pharyngitis but only 50% after skin infection), elevated anti-DNase B (more sensitive after skin infections), and streptozyme test. Complement levels show characteristically low C3 (>90% of cases) with normal C4, reflecting alternative pathway activation; C3 normalizes within 6-8 weeks and persistent hypocomplementemia beyond 8-12 weeks should prompt consideration of alternative diagnoses (C3 glomerulopathy, lupus nephritis). Urinalysis shows dysmorphic RBCs, RBC casts, mild proteinuria, and occasionally white blood cells. Renal biopsy is not routinely performed but is indicated for atypical features (normal complement, persistent renal dysfunction beyond 4 weeks, nephrotic-range proteinuria, age <2 or >40 years); biopsy shows diffuse endocapillary proliferative GN with subepithelial 'humps' on EM. | Treatment is supportive, as no specific therapy alters the course of PSGN. Sodium and fluid restriction (1-2 g sodium/day, fluid restriction to insensible losses plus urine output) to manage volume overload and hypertension. Loop diuretics (furosemide 1-2 mg/kg IV or PO every 6-12 hours) for volume overload, edema, hypertension, and pulmonary congestion. Antihypertensive agents including calcium channel blockers (nifedipine 0.25-0.5 mg/kg/dose) or ACE inhibitors are used for persistent hypertension after volume control. Antibiotic therapy (penicillin V 250-500 mg four times daily for 10 days, or a single dose of benzathine penicillin 1.2 million units IM) is given to eradicate any remaining streptococcal infection and prevent transmission of nephritogenic strains, though it does not alter the course of established nephritis. Dialysis is rarely required (1-2% of children, higher in adults) for severe oliguria, volume overload refractory to diuretics, or hyperkalemia. Household contacts should be screened and treated for streptococcal infection. Immunosuppressive therapy is not indicated. | Good - Excellent prognosis in children, with >95% achieving full recovery. Gross hematuria resolves within 1-2 weeks, edema and hypertension resolve within 1-2 weeks, and serum creatinine normalizes within 3-4 weeks. Microscopic hematuria may persist for 1-2 years and mild proteinuria for 2-3 years, both of which eventually resolve in the vast majority. C3 normalizes within 6-8 weeks. Fewer than 1-2% of children develop chronic kidney disease or ESRD. In adults, the prognosis is less favorable: 25-50% may have persistent urinary abnormalities, 10-20% develop chronic kidney disease, and 1-3% may progress to ESRD, particularly elderly patients. Recurrence is extremely rare because infection with a specific nephritogenic strain confers type-specific immunity. During epidemics, the attack rate among individuals infected with nephritogenic strains is approximately 10-15%. | N00.9 |
| 17 | 16 | Rapidly Progressive Glomerulonephritis (RPGN) | Glomerular Diseases | RPGN is a clinical syndrome characterized by rapid loss of renal function (typically >50% decline in GFR within days to weeks) with pathologic evidence of crescentic glomerulonephritis (crescents in >50% of glomeruli on biopsy). Crescents are formed by proliferation of parietal epithelial cells and infiltrating monocytes/macrophages in Bowman's space, triggered by rupture of the GBM and fibrin extravasation into Bowman's space. RPGN is classified by immunofluorescence pattern into three types: Type I (anti-GBM antibody disease, 10-20% of cases) shows linear IgG staining along the GBM; Type II (immune complex-mediated, 40-45%) shows granular immune deposits and is caused by SLE, IgA nephropathy, PSGN, MPGN, or other immune complex diseases; Type III (pauci-immune, 40-50%) shows absent or scanty immune deposits and is almost always associated with ANCA positivity (MPO-ANCA or PR3-ANCA), representing the renal manifestation of ANCA-associated vasculitis. The common final pathway involves severe glomerular inflammation, necrosis of capillary walls, breaks in the GBM, fibrin deposition in Bowman's space, and crescent formation. Cellular crescents may progress to fibrocellular and then fibrous crescents over days to weeks, transitioning from potentially reversible to irreversible glomerular damage. | RPGN accounts for approximately 2-5% of all glomerulonephritis in renal biopsy series. The exact incidence varies by etiology: anti-GBM disease occurs in 0.5-1.0 per million/year, ANCA-associated vasculitis renal involvement occurs in 3-5 per million/year, and immune complex crescentic GN depends on the underlying disease. RPGN is more common in adults than children. Pauci-immune crescentic GN (ANCA-associated) is the most common cause in adults over 50 years. The overall prognosis is significantly worse than non-crescentic GN, making RPGN a nephrology emergency. | The age at onset depends on the underlying etiology. Anti-GBM RPGN has a bimodal age distribution (young adults 20-30 and elderly 60-70). Pauci-immune (ANCA-associated) RPGN most commonly affects adults over 50-60 years, with a peak incidence in the seventh decade. Immune complex-mediated RPGN can occur at any age depending on the underlying disease (lupus nephritis in young adults, PSGN in children). Pediatric RPGN is uncommon and is most often immune complex-mediated. | Rapidly progressive decline in renal function over days to weeks is the defining feature, manifesting as oliguria, rapidly rising serum creatinine, and uremic symptoms (nausea, vomiting, anorexia, confusion). Active urinary sediment with dysmorphic red blood cells, red blood cell casts, and proteinuria (variable, non-nephrotic to nephrotic) is characteristic. Gross hematuria (tea-colored or cola-colored urine) is present in 30-50% of patients. Hypertension may be present but is not as prominent as in PSGN. Systemic symptoms depend on the underlying etiology: pulmonary hemorrhage in anti-GBM disease and ANCA vasculitis, malar rash and joint pain in lupus, purpura and sinusitis in granulomatosis with polyangiitis. Fever, malaise, weight loss, and myalgias are common in ANCA-associated RPGN. Without treatment, complete anuria and dialysis-dependent renal failure develop within days to weeks. | Kidneys (glomeruli - crescentic inflammation and necrosis); lungs (alveolar hemorrhage in anti-GBM and ANCA vasculitis); upper airways (sinusitis, epistaxis in GPA); skin (purpura in vasculitis); joints (arthralgia); peripheral nerves (mononeuritis multiplex in vasculitis) | Urgent renal biopsy is the cornerstone of diagnosis, demonstrating crescents in more than 50% of glomeruli (often >80% in severe disease). The immunofluorescence pattern classifies the type: linear IgG (anti-GBM), granular deposits (immune complex), or pauci-immune (ANCA-associated). Serologic testing should be performed emergently: anti-GBM antibodies, ANCA (MPO and PR3 by ELISA), ANA, anti-dsDNA, complement levels (C3, C4). Urinalysis shows active sediment with dysmorphic RBCs and casts. Serum creatinine at presentation and the percentage of fibrous (vs. cellular) crescents on biopsy are the strongest predictors of renal recovery. Chest X-ray or CT should be performed to evaluate for pulmonary hemorrhage. Complete blood count may show anemia disproportionate to renal failure if pulmonary hemorrhage is present. CRP and ESR are elevated in vasculitis. | RPGN is a nephrology emergency requiring immediate treatment. Treatment depends on the underlying cause (see specific disease entries for anti-GBM, ANCA vasculitis, and lupus nephritis). General principles include aggressive immunosuppression with IV pulse methylprednisolone (500-1000 mg/day for 3 days) as the immediate first step for all types. For pauci-immune/ANCA-associated RPGN: rituximab (375 mg/m2 weekly x 4 or 1 g x 2) or cyclophosphamide (15 mg/kg IV every 2 weeks x 3 then every 3 weeks, or 2 mg/kg/day orally) combined with corticosteroids; plasma exchange may be added for severe disease (creatinine >5.8 mg/dL) based on PEXIVAS trial subset analysis. For anti-GBM RPGN: plasmapheresis plus cyclophosphamide and corticosteroids. For immune complex RPGN: treatment of the underlying disease (e.g., lupus induction therapy). Dialysis support as needed. Early treatment when cellular crescents predominate offers the best chance of renal recovery, as fibrous crescents represent irreversible damage. | Poor - Prognosis depends on the underlying etiology, percentage of crescentic glomeruli, proportion of cellular vs. fibrous crescents, and serum creatinine at presentation. Patients presenting with creatinine <5 mg/dL and predominantly cellular crescents have the best renal prognosis (60-80% renal recovery). Those requiring dialysis at presentation have a 20-40% chance of renal recovery (better for ANCA-associated than anti-GBM disease). Anti-GBM RPGN has the worst prognosis if dialysis-dependent at presentation (<8-15% renal recovery). ANCA-associated RPGN has better potential for recovery even in severe disease (30-50% can discontinue dialysis with aggressive treatment). Immune complex-mediated RPGN prognosis varies by underlying disease. Without treatment, RPGN progresses to irreversible ESRD within weeks. Long-term renal survival with treatment is 60-80% at 5 years for ANCA-associated RPGN. | N01.9 |
| 18 | 17 | Thin Basement Membrane Disease | Glomerular Diseases | Thin basement membrane disease (TBMD), also known as thin basement membrane nephropathy or benign familial hematuria, is characterized by diffuse thinning of the glomerular basement membrane below the age-adjusted normal range (typically <250 nm in adults, compared to the normal 300-400 nm). The most common cause is heterozygous mutations in COL4A3 or COL4A4 genes (encoding the alpha-3 and alpha-4 chains of type IV collagen), which are the same genes involved in autosomal recessive Alport syndrome. TBMD is now recognized as the heterozygous carrier state of autosomal recessive Alport syndrome in many cases, and is increasingly referred to as 'heterozygous COL4A3/COL4A4-associated nephropathy.' The GBM thinning results from reduced incorporation of the alpha-3-4-5 collagen IV network into the basement membrane. In most patients, the thin GBM allows passage of red blood cells into the urinary space without significant proteinuria or progressive kidney disease. However, recent long-term studies have shown that 10-20% of patients with TBMD develop progressive proteinuria and CKD, particularly when additional risk factors are present (hypertension, obesity, second genetic hit, female sex, advancing age). TBMD may coexist with IgA nephropathy or other glomerular diseases. | TBMD is very common, estimated to affect 1% of the general population (5-9% in some populations based on screening studies), making it one of the most common inherited renal conditions. It accounts for 20-25% of persistent microscopic hematuria in children and 5-10% in adults undergoing renal biopsy for isolated hematuria. The condition is found worldwide across all ethnic groups. There is no significant gender predilection in prevalence, though females may be more frequently diagnosed because they are more likely to undergo urinalysis. Heterozygous COL4A3/A4 mutations are found in approximately 40-50% of patients with biopsy-proven TBMD. | TBMD is present from birth but typically detected when incidental microscopic hematuria is discovered on routine urinalysis at any age, from childhood through adulthood. There is no specific age of onset of symptoms; rather, hematuria is a lifelong finding that is detected at the time of first urinalysis. Episodes of gross hematuria may occur during childhood, often triggered by upper respiratory infections, similar to IgA nephropathy. Most patients are diagnosed in childhood or young adulthood when hematuria is incidentally discovered. | Persistent microscopic hematuria is the hallmark and often the only clinical finding. The hematuria is typically asymptomatic and discovered incidentally on routine urinalysis. Episodes of gross hematuria may occur, particularly in children and young adults, often precipitated by upper respiratory infections or exercise. Proteinuria is typically absent or minimal (<500 mg/day) in most patients, though 10-15% develop proteinuria over time. Blood pressure is typically normal. Renal function (eGFR) is normal in the vast majority of patients at diagnosis. Family history of microscopic hematuria without progressive CKD or hearing loss is common and suggestive of TBMD rather than Alport syndrome. Hearing loss and ocular abnormalities are absent (distinguishing from Alport syndrome). | Kidneys (glomerular basement membrane); no extrarenal manifestations (distinguishing from Alport syndrome) | The diagnosis of TBMD requires renal biopsy with electron microscopy demonstrating diffusely thin GBM (<250 nm in adults, with age-appropriate thresholds in children). Light microscopy is normal or shows only minor nonspecific changes. Immunofluorescence is negative. Collagen IV alpha-chain immunohistochemistry should be performed to exclude Alport syndrome: in TBMD, alpha-3, alpha-4, and alpha-5 chains are preserved in the GBM and Bowman's capsule. Genetic testing of COL4A3, COL4A4, and COL4A5 is increasingly recommended, particularly when the biopsy findings are borderline, there is a family history of renal failure or hearing loss, or proteinuria is present. Urinalysis consistently shows microscopic hematuria with dysmorphic red blood cells. Family members should be screened with urinalysis. Audiometry is recommended to exclude subclinical hearing loss associated with Alport syndrome. | Most patients with TBMD require no specific treatment beyond reassurance and periodic monitoring. Annual monitoring of blood pressure, serum creatinine/eGFR, and urinalysis (with quantification of proteinuria if present) is recommended lifelong, as a subset of patients may develop progressive disease over decades. If proteinuria develops (>300 mg/day), ACE inhibitors (ramipril 2.5-10 mg daily) or ARBs (losartan 50-100 mg daily) should be initiated for renoprotection, similar to Alport syndrome management. Blood pressure should be maintained below 130/80 mmHg. General nephroprotective measures including avoidance of nephrotoxins, adequate hydration, and cardiovascular risk factor management are recommended. Genetic counseling is important, particularly regarding the risk of Alport syndrome in offspring if both parents carry COL4A3/A4 mutations or if one parent carries a COL4A5 mutation. | Good - The prognosis is excellent for the majority of patients, with stable renal function throughout life. The traditional view that TBMD is entirely benign has been modified: long-term studies show that 10-20% of patients develop progressive proteinuria and 5-8% develop CKD (usually mild, stage 2-3) over several decades, particularly women over 40 years and patients with additional risk factors. Progression to ESRD is very rare (<1%) but has been reported, particularly in patients with compound heterozygous COL4A3/A4 mutations or digenic mutations. Life expectancy is normal. The identification of specific COL4A3/A4 mutations may help prognosticate: certain missense mutations carry higher risk of progression than nonsense mutations. Genetic counseling regarding reproductive risk is important given the relationship to Alport syndrome. | N02.9 |
| 19 | ▸ Tubular & Interstitial Diseases | |||||||||||
| 20 | 18 | Acute Interstitial Nephritis (AIN) | Tubular & Interstitial Diseases | AIN is an immune-mediated inflammatory condition affecting the renal tubulointerstitium, most commonly caused by drug hypersensitivity reactions. Drug-induced AIN accounts for 70-75% of cases, with the most common causative agents being antibiotics (penicillins, cephalosporins, sulfonamides, fluoroquinolones, rifampin), proton pump inhibitors (PPIs, increasingly recognized as the most common cause in recent series), NSAIDs, allopurinol, and immune checkpoint inhibitors (pembrolizumab, nivolumab). The pathogenesis involves a delayed-type (type IV) hypersensitivity reaction: the drug or its metabolite acts as a hapten, binding to tubular basement membrane proteins and being processed by antigen-presenting cells, which activate CD4+ and CD8+ T cells that infiltrate the interstitium and cause tubular injury. The interstitial infiltrate characteristically contains T lymphocytes (CD4+ and CD8+), macrophages, and variable numbers of eosinophils (prominent in drug-induced AIN). Other causes include infections (Legionella, Leptospira, CMV, EBV, Hantavirus), autoimmune diseases (SLE, Sjogren syndrome, sarcoidosis, IgG4-related disease), and tubulointerstitial nephritis with uveitis (TINU) syndrome. Non-caseating granulomas are found in 15-20% of AIN biopsies, particularly with sarcoidosis, TINU, and certain drugs. | AIN accounts for approximately 15-20% of AKI in hospitalized patients and 1-3% of all renal biopsies. The true incidence is likely underestimated because many cases are not biopsied. Drug-induced AIN is the most common form. PPI-associated AIN has become increasingly recognized, with PPIs now implicated in 12-20% of drug-induced AIN cases. Immune checkpoint inhibitor-associated AIN occurs in 1-5% of patients receiving these cancer therapies. Infection-associated AIN is less common in developed countries. There is no significant gender predilection. AIN can occur at any age but is more common in elderly patients due to polypharmacy. | Drug-induced AIN can occur at any age but is more common in older adults due to polypharmacy and age-related changes in drug metabolism. PPI-induced AIN is typically seen in adults, with a mean age of 60-70 years. TINU syndrome predominantly affects adolescents and young adults (median age 15-20 years). Immune checkpoint inhibitor AIN occurs in cancer patients, typically middle-aged to elderly adults. Infection-associated AIN can occur at any age. | The classic triad of drug-induced AIN is fever, rash, and eosinophilia, but this complete triad is present in only 10-15% of cases. Rising serum creatinine over days to weeks is the primary finding. Fever occurs in 25-40% of drug-induced AIN. Maculopapular skin rash is present in 15-25%. Eosinophilia is found in 30-50% of drug-induced cases. Arthralgias may accompany the allergic reaction. Non-oliguric AKI is more common than oliguric. Flank pain from renal swelling may be reported. Urine may show white blood cells, white blood cell casts, and mild proteinuria (usually <1 g/day). Eosinophiluria (Hansel stain positive) is suggestive but not specific. PPI-induced AIN characteristically has a delayed onset (weeks to months after drug initiation) and often lacks the classic allergic features. Immune checkpoint inhibitor AIN may present with other immune-related adverse events. | Kidneys (tubulointerstitium - inflammatory infiltrate, tubulitis); may have systemic features of drug hypersensitivity; eyes (uveitis in TINU syndrome); lungs and lymph nodes (in sarcoidosis); multiple organs (in IgG4-related disease) | Clinical suspicion based on temporal relationship between drug exposure and AKI is the key to diagnosis. Urinalysis may show sterile pyuria (WBCs without bacteria), WBC casts, mild proteinuria, and sometimes eosinophiluria (>1% eosinophils on Hansel stain, present in 40-60% of drug-induced AIN). Serum eosinophilia supports the diagnosis when present. Renal biopsy is the gold standard and is recommended when the diagnosis is uncertain, renal function does not improve after drug withdrawal, or empiric steroid therapy is being considered. Biopsy shows interstitial edema with inflammatory cell infiltrate (T lymphocytes, macrophages, eosinophils), tubulitis (lymphocytic invasion of tubular epithelium), and relative sparing of glomeruli and vessels. Gallium-67 scintigraphy may show diffuse bilateral uptake in AIN but is neither sensitive nor specific. Renal ultrasound shows normal or enlarged kidneys. Serum IgG4 levels should be checked if IgG4-related disease is suspected. | Withdrawal of the offending drug is the most important therapeutic step and should be done immediately upon suspicion of AIN. Renal function improves in approximately 60-70% of patients within 1-2 weeks of drug withdrawal alone. Corticosteroid therapy (prednisone 1 mg/kg/day for 1-2 weeks, then tapered over 4-8 weeks) is recommended when renal function does not improve within 5-7 days of drug withdrawal, or if biopsy shows active interstitial inflammation without significant fibrosis. Earlier initiation of steroids (within the first 2 weeks of AKI) is associated with better renal recovery. PPI-induced AIN may require longer steroid courses due to the chronic nature of the exposure. Mycophenolate mofetil (1-2 g/day) has been used for steroid-resistant cases. Immune checkpoint inhibitor AIN is managed with corticosteroids (prednisone 0.5-1 mg/kg/day), with consideration of holding the checkpoint inhibitor depending on renal response and oncologic needs. TINU syndrome requires both corticosteroids for renal disease and topical or systemic steroids for uveitis. | Variable - Prognosis depends on the duration of drug exposure before recognition, extent of interstitial fibrosis at diagnosis, and promptness of treatment. Complete or partial renal recovery occurs in 60-70% of patients after drug withdrawal alone and in 70-85% with additional corticosteroid therapy. Patients diagnosed and treated early (within 2 weeks of AKI onset) have significantly better outcomes than those with delayed recognition. Persistent CKD develops in 30-40% of patients, particularly those with prolonged drug exposure, delayed diagnosis, or significant interstitial fibrosis on biopsy. NSAID-induced AIN has worse renal recovery compared to antibiotic-induced AIN. PPI-induced AIN may have an insidious course with chronic tubulointerstitial injury if unrecognized. Immune checkpoint inhibitor AIN generally responds well to steroids, with 50-80% achieving renal recovery. | N10 |
| 21 | 19 | Acute Tubular Necrosis (ATN) | Tubular & Interstitial Diseases | ATN is the most common cause of intrinsic acute kidney injury, resulting from ischemic or nephrotoxic injury to renal tubular epithelial cells, predominantly in the proximal tubule (S3 segment) and thick ascending limb of Henle. Ischemic ATN occurs when renal perfusion falls below the autoregulatory threshold, causing tubular cell ATP depletion, loss of cell polarity, cytoskeletal disruption, and detachment from the basement membrane. The outer medulla is particularly vulnerable due to its low oxygen tension and high metabolic demand. Nephrotoxic ATN is caused by direct tubular cell injury from drugs (aminoglycosides, cisplatin, amphotericin B, contrast agents), endogenous toxins (myoglobin, hemoglobin, myeloma light chains), or environmental toxins. The pathophysiology involves tubular obstruction by sloughed cells and debris, backleak of filtrate through denuded basement membrane, afferent arteriolar vasoconstriction mediated by tubuloglomerular feedback, and reduced glomerular ultrafiltration coefficient. Recovery occurs through surviving tubular cell dedifferentiation, proliferation, and re-differentiation to restore tubular integrity. | ATN is the most common cause of intrinsic AKI, accounting for approximately 45-50% of all AKI cases in hospitalized patients. Hospital-acquired AKI affects 5-7% of all hospitalized patients and 30-50% of ICU patients, with ATN being the predominant cause. The incidence has been increasing due to aging populations, increasing comorbidities, and greater use of nephrotoxic medications and contrast agents. Mortality rates for ATN requiring dialysis remain high at 40-60% in ICU settings, though this largely reflects the severity of the underlying illness. ATN is the most common cause of AKI requiring renal replacement therapy. | ATN can occur at any age but is most common in elderly patients and those with pre-existing risk factors. Hospital-acquired ATN peaks in the seventh to eighth decade due to age-related decline in renal reserve and increased comorbidities. Pediatric ATN is less common but occurs in neonates (perinatal asphyxia, sepsis) and children with major surgery, sepsis, or nephrotoxin exposure. Aminoglycoside-induced ATN is more common in elderly patients with reduced GFR. | Oliguria (urine output <400 mL/day) is present in approximately 50-60% of ATN cases (oliguric ATN), while 40-50% maintain relatively preserved urine output (non-oliguric ATN, which carries better prognosis). Rising serum creatinine and BUN over hours to days is the hallmark laboratory finding. Urine is characteristically dilute with low specific gravity (<1.015) and low osmolality (<350 mOsm/kg), reflecting loss of tubular concentrating ability. Muddy brown granular casts and renal tubular epithelial cells in urinary sediment are characteristic findings. Fractional excretion of sodium (FENa) is typically >2% (reflecting impaired tubular sodium reabsorption), helping distinguish ATN from pre-renal AKI. Hyperkalemia, metabolic acidosis, and hyperphosphatemia develop as renal function deteriorates. Volume overload with peripheral edema and pulmonary congestion may develop in oliguric patients. Uremic symptoms (nausea, anorexia, confusion) occur in severe cases. | Kidneys (proximal tubules S3 segment, thick ascending limb of Henle, outer medulla); systemic effects from AKI (electrolyte imbalance, volume overload, uremia) | Diagnosis is primarily clinical based on the context (ischemic or nephrotoxic insult) and characteristic laboratory findings. Urinalysis shows muddy brown granular casts (pathognomonic), renal tubular epithelial cells, and low specific gravity. FENa >2% and FEUrea >35% help distinguish ATN from pre-renal AKI (though FENa may be <1% in early ATN or contrast/myoglobin-induced ATN). Serum creatinine rises 0.3-0.5 mg/dL per day in non-catabolic ATN and up to 1-2 mg/dL per day in catabolic states. NGAL (neutrophil gelatinase-associated lipocalin), KIM-1, and TIMP-2/IGFBP7 are emerging biomarkers for early ATN detection. Renal ultrasound shows normal-sized kidneys with preserved cortical thickness and may demonstrate increased cortical echogenicity. Renal biopsy is rarely needed but may be indicated when the diagnosis is uncertain or recovery is delayed beyond 2-3 weeks. | Treatment is primarily supportive with removal or treatment of the underlying cause. Volume resuscitation with isotonic crystalloids for ischemic ATN from hypovolemia. Discontinuation of nephrotoxic medications. Maintenance of euvolemia and hemodynamic optimization (MAP >65 mmHg). Loop diuretics (furosemide 40-200 mg IV) may convert oliguric to non-oliguric ATN, facilitating volume management, but do not accelerate recovery or improve outcomes. Renal replacement therapy (continuous venovenous hemofiltration in hemodynamically unstable ICU patients, or intermittent hemodialysis in stable patients) is indicated for severe hyperkalemia (>6.5 mEq/L), refractory metabolic acidosis, volume overload unresponsive to diuretics, and uremic complications (pericarditis, encephalopathy). Electrolyte management: hyperkalemia treated with insulin-dextrose, calcium gluconate, sodium bicarbonate, and kayexalate. Avoid further nephrotoxic agents. Dosing adjustment for all renally cleared medications. | Variable - ATN is potentially reversible, with renal recovery occurring in 50-70% of patients who survive the underlying illness. Recovery typically begins within 1-3 weeks, heralded by a diuretic phase with increasing urine output. Non-oliguric ATN has a better prognosis than oliguric ATN (mortality 25-30% vs. 50-60%). Complete recovery of renal function to baseline occurs in approximately 60-70% of survivors. However, 20-30% of survivors have persistent CKD, and 5-10% require long-term dialysis. Hospital mortality for ATN requiring dialysis in ICU settings remains 40-60%. Each episode of AKI increases the risk of subsequent CKD progression. Prolonged ATN (>3 weeks without recovery) suggests cortical necrosis or severe tubular injury with permanent nephron loss. | N17.0 |
| 22 | 20 | Aristolochic Acid Nephropathy (Chinese Herb Nephropathy) | Tubular & Interstitial Diseases | Aristolochic acid nephropathy (AAN), originally described as Chinese herb nephropathy, is a progressive tubulointerstitial nephritis caused by exposure to aristolochic acid contained in plants of the Aristolochia and Asarum genera used in traditional Chinese medicine and other herbal remedies worldwide. The condition was first identified in 1993 in a cohort of Belgian women who developed rapidly progressive renal failure after taking a slimming regimen containing Aristolochia fangchi (inadvertently substituted for Stephania tetrandra). The pathogenesis is identical to Balkan endemic nephropathy: aristolochic acid is metabolized to reactive aristolactam nitrenium ions that form covalent DNA adducts with genomic DNA, causing tubular cell necrosis, interstitial fibrosis, and characteristic A:T to T:A transversion mutations in TP53 and other genes. Unlike BEN (which involves chronic low-dose exposure over decades), AAN from herbal remedies often involves higher acute doses over shorter periods, leading to more rapid progression. The IARC has classified aristolochic acid as a Group 1 carcinogen. AAN is associated with a high risk (40-46%) of urothelial carcinoma of the renal pelvis or ureter. The condition affects individuals worldwide who use aristolochic acid-containing herbal products, including traditional Chinese medicine, Kampo (Japanese), and Ayurvedic preparations. | The true global prevalence of AAN is unknown but is likely substantial given the widespread use of aristolochic acid-containing herbs in traditional medicine systems serving billions of people. The Belgian cohort identified approximately 100 affected individuals from a single weight-loss clinic. In Taiwan, where Aristolochia-containing herbal products were widely used, an estimated one-third of the population had been exposed to AA-containing herbs, and studies have linked this exposure to the island's exceptionally high incidence of upper urinary tract urothelial carcinoma. In China, AA-containing herbs are prescribed to millions of patients annually, though regulatory restrictions are being implemented. AAN is increasingly recognized in the UK, Japan, Korea, and other countries where Chinese herbal medicine is practiced. | AAN from herbal remedy exposure can occur at any age, depending on when the aristolochic acid-containing products are consumed. The Belgian cohort affected young to middle-aged women (mean age approximately 45 years). In Asia, where herbal medicine use is lifelong, exposure may begin in childhood. The latency period from exposure to clinical nephropathy is variable, ranging from months (high-dose acute exposure) to years (chronic low-dose exposure). Urothelial carcinoma may develop years to decades after initial exposure. | Rapidly progressive or gradually declining renal function is the primary clinical feature, depending on the dose and duration of AA exposure. Anemia is prominent and often disproportionate to the degree of renal impairment. Proteinuria is mild and tubular in pattern. Urinary sediment is characteristically bland. Hypertension is typically mild or absent. The kidneys are bilaterally small and smooth on imaging. In the Belgian cohort, renal function declined rapidly, with many patients reaching ESRD within 1-2 years of herbal exposure. Gastrointestinal symptoms from concurrent herbal toxicity may be present. There is a high risk of upper urinary tract urothelial carcinoma (40-46% in the Belgian cohort at the time of prophylactic nephroureterectomy). | Kidneys (tubulointerstitium - extensive fibrosis; tubular atrophy); upper urinary tract urothelium (urothelial carcinoma, 40-46%); bladder urothelium (transitional cell carcinoma risk) | Diagnosis requires a high index of suspicion and thorough herbal medication history. Identification of AA-containing herbs in the patient's medicinal history is critical. Renal biopsy shows severe tubulointerstitial fibrosis and tubular atrophy with minimal glomerular changes, similar to BEN. Detection of AA-DNA adducts in renal cortex or urothelial tissue by mass spectrometry confirms AA exposure. Characteristic TP53 A:T to T:A transversion mutations in urothelial tissue are highly specific for AA exposure. Renal ultrasound or CT shows bilaterally small, smooth kidneys. Urinalysis shows mild tubular proteinuria. Urine cytology for screening of urothelial carcinoma. CT urography for upper tract surveillance. Analysis of suspected herbal products by mass spectrometry can identify AA contamination. | Immediate cessation of all aristolochic acid-containing herbal products is essential. There is no specific antidote or disease-modifying therapy. Supportive CKD management: blood pressure control, anemia management with erythropoiesis-stimulating agents, metabolic bone disease management, and dietary modifications. Corticosteroids have been tried without convincing evidence of benefit. Renal replacement therapy for ESRD. Prophylactic bilateral nephroureterectomy should be considered at the time of kidney transplantation or dialysis initiation due to the very high risk (40-46%) of urothelial carcinoma in the retained native upper tracts. Lifelong surveillance for urothelial carcinoma including bladder cystoscopy and urine cytology every 6-12 months. Public health measures include regulation and labeling of herbal products, educational campaigns about the dangers of AA-containing herbs, and pharmacovigilance programs. | Poor - AAN has a poor renal prognosis, with many patients progressing to ESRD within 1-5 years of significant AA exposure. The rate of progression correlates with the cumulative dose of AA ingested. Once established, interstitial fibrosis is irreversible. The major additional risk is urothelial carcinoma: in the Belgian cohort, 40-46% had urothelial carcinoma at the time of prophylactic nephroureterectomy, often multifocal and bilateral. Kidney transplant outcomes are generally good provided native tract nephroureterectomy is performed. Bladder cancer surveillance must continue lifelong. The prognosis for detected urothelial carcinoma depends on stage and grade. With increasing awareness and regulation, the incidence of new AAN cases may decline, but the risk to previously exposed individuals persists for decades. | N14.1 |
| 23 | 21 | Balkan Endemic Nephropathy | Tubular & Interstitial Diseases | Balkan endemic nephropathy (BEN) is a chronic tubulointerstitial nephropathy confined to specific rural communities in the Balkan countries (Serbia, Bosnia, Croatia, Bulgaria, Romania) along the tributaries of the Danube River. The disease is caused by chronic dietary exposure to aristolochic acid (AA), a potent nephrotoxin and carcinogen produced by Aristolochia clematitis, a plant whose seeds contaminate wheat grain harvested from fields where it grows as a weed. AA is absorbed from contaminated flour products and selectively concentrated in the renal cortex, where it forms covalent DNA adducts (aristolactam-deoxyadenosine and aristolactam-deoxyguanosine) with genomic DNA in tubular epithelial cells. These adducts cause characteristic A:T to T:A transversion mutations, including in the TP53 tumor suppressor gene (codon 139 hotspot), and trigger tubular cell apoptosis, chronic tubulointerstitial inflammation, and progressive fibrosis. The strong association between BEN and upper urinary tract urothelial carcinoma (occurring in 30-40% of BEN patients) is explained by the mutagenic properties of AA-DNA adducts in the urothelium. The disease clusters in households and communities reflect shared dietary exposure rather than genetic transmission, although genetic polymorphisms in detoxification enzymes (NAT, CYP1A) may influence individual susceptibility. | BEN affects an estimated 25,000-100,000 people in endemic regions along the Danube River tributaries, with the highest prevalence in specific villages in Serbia, Bulgaria, and Romania. Prevalence in endemic villages ranges from 2-10% of the adult population. The incidence has been declining over recent decades due to changes in agricultural practices, urbanization, and awareness of the contamination source. Upper urinary tract urothelial carcinoma incidence in endemic regions is 100-200 times higher than in non-endemic areas. BEN is found exclusively in the Balkans, unlike aristolochic acid nephropathy from Chinese herbal medicine which occurs worldwide. | BEN typically presents insidiously in the fourth to sixth decade of life, with a long preclinical phase. The disease is rarely diagnosed before age 30, despite likely exposure beginning in childhood. The peak age of diagnosis is 40-60 years. ESRD develops at a mean age of 55-65 years. Upper urinary tract urothelial carcinoma may present concurrently with or after the diagnosis of nephropathy. | BEN has an insidious onset with gradually progressive CKD. Early symptoms include fatigue, pallor (anemia), and mild polyuria from concentrating defect. Proteinuria is characteristically mild and tubular in pattern (beta-2 microglobulin, alpha-1 microglobulin). Urinary sediment is bland without hematuria (unless urothelial carcinoma is present). Hypertension is typically absent or mild, even in advanced CKD, which is an important distinguishing feature from other causes of CKD. Anemia is often severe and disproportionate to the degree of renal impairment, reflecting reduced erythropoietin production from the damaged interstitium. Progressive decline in renal function over 5-15 years leading to ESRD. Bilateral small kidneys on imaging. Gross hematuria or flank pain should raise concern for complicating upper urinary tract urothelial carcinoma. | Kidneys (tubulointerstitium - progressive fibrosis and tubular atrophy; small bilateral kidneys); upper urinary tract urothelium (urothelial carcinoma in 30-40%); ureters and renal pelvis (transitional cell carcinoma) | Diagnosis is primarily epidemiologic and clinical, based on residence in an endemic region, family history of CKD, and characteristic clinical features. Renal ultrasound shows bilaterally small kidneys with smooth contours and increased cortical echogenicity. Urinalysis shows mild tubular proteinuria without significant hematuria (unless urothelial carcinoma is present). Biomarkers of AA exposure: detection of AA-DNA adducts in renal cortex tissue (by LC-MS/MS) or urothelial tissue is the gold standard for confirming AA exposure. Characteristic TP53 mutations (A:T to T:A transversions) in urothelial tissue are specific for AA exposure. Renal biopsy shows severe tubulointerstitial fibrosis with tubular atrophy, thickened tubular basement membranes, and minimal glomerular or vascular changes. Regular screening for upper urinary tract urothelial carcinoma is essential: urine cytology every 6-12 months, CT urography or retrograde urography annually. Cystoscopy and ureteroscopy if abnormalities are detected. | There is no specific therapy to reverse BEN. Prevention through elimination of AA exposure (removing Aristolochia from wheat fields, improved grain sorting) is the primary public health measure. Supportive CKD management: ACE inhibitors or ARBs for hypertension and proteinuria, correction of anemia with erythropoiesis-stimulating agents, management of metabolic complications (acidosis, bone disease, electrolytes). Renal replacement therapy (hemodialysis or peritoneal dialysis) for ESRD. Kidney transplantation is feasible but requires bilateral nephroureterectomy prior to or at the time of transplantation to eliminate the risk of urothelial carcinoma in the retained native upper tract. Surveillance for urothelial carcinoma must continue lifelong, including after kidney transplantation, as cancers may arise in residual urothelium (bladder). Treatment of urothelial carcinoma follows standard oncologic protocols with nephroureterectomy and adjuvant chemotherapy. | Poor - BEN is a progressive disease with inevitable progression to ESRD over 5-15 years. The rate of GFR decline is approximately 3-5 mL/min/year. Five-year survival on dialysis is comparable to other causes of ESRD. The major additional risk is upper urinary tract urothelial carcinoma, which develops in 30-40% of BEN patients and is often bilateral and multifocal. Urothelial carcinoma in BEN patients has a similar stage-for-stage prognosis to sporadic upper tract TCC. With declining exposure to contaminated grain, the incidence of BEN has been decreasing in endemic regions. Kidney transplant outcomes are good provided adequate cancer screening and native nephroureterectomy are performed. | N15.0 |
| 24 | 22 | Bartter Syndrome | Tubular & Interstitial Diseases | Bartter syndrome is a group of rare autosomal recessive salt-wasting tubulopathies caused by defective sodium chloride reabsorption in the thick ascending limb (TAL) of Henle's loop, resulting in a clinical picture resembling chronic loop diuretic use. Five genetic types have been identified: Type 1 (SLC12A1, encoding NKCC2 Na-K-2Cl cotransporter), Type 2 (KCNJ1, encoding ROMK potassium channel), Type 3 (CLCNKB, encoding ClC-Kb chloride channel), Type 4a (BSND, encoding barttin, a chloride channel subunit), and Type 4b (combined CLCNKA and CLCNKB mutations). The NKCC2 cotransporter in the apical membrane of TAL cells mediates electroneutral uptake of Na+, K+, and 2Cl- from the tubular lumen; potassium recycling through apical ROMK generates a lumen-positive potential that drives paracellular calcium and magnesium reabsorption. Loss of function of any component of this system causes NaCl wasting, volume contraction, stimulation of the renin-angiotensin-aldosterone system, hypokalemia (from aldosterone-driven distal potassium secretion), metabolic alkalosis (from hydrogen ion loss in exchange for sodium reabsorption in the collecting duct), and hypercalciuria (from loss of the lumen-positive potential driving paracellular calcium absorption). Type 4a/4b additionally causes sensorineural hearing loss because barttin and ClC-Ka/Kb are expressed in the stria vascularis of the inner ear. | Bartter syndrome is rare, with an estimated incidence of approximately 1 per 1,000,000 live births, though prevalence is higher in consanguineous populations. Type 3 (ClC-Kb mutations) is the most common form globally. Types 1 and 2 (antenatal/neonatal Bartter syndrome) are the most severe. The disease has been described worldwide in all ethnic groups. The total number of reported cases is in the low thousands. Carrier frequency in the general population is estimated at approximately 1 in 500. | Types 1 and 2 present in the antenatal/neonatal period with polyhydramnios (due to fetal polyuria), premature birth, and severe salt wasting in the newborn period. Type 3 (classic Bartter syndrome) typically presents in infancy to early childhood with failure to thrive, polyuria, and polydipsia, though milder cases may not present until adolescence or adulthood. Type 4 presents in the neonatal period with additional sensorineural hearing loss. Types 4b may present in the fetal period with severe polyhydramnios. | Polyuria and polydipsia from impaired urinary concentrating ability are universal features. Failure to thrive and growth retardation in children. Salt craving is common. Muscle weakness, cramping, and tetany from hypokalemia and metabolic alkalosis. Volume depletion despite normal or increased fluid intake, with low-normal blood pressure or hypotension. Neonatal Bartter syndrome (types 1, 2, 4) presents with life-threatening salt and water losses, dehydration, and fever. Nephrocalcinosis from hypercalciuria is characteristic of types 1 and 2, and may cause flank pain. Sensorineural hearing loss in types 4a and 4b. Characteristic facial appearance in some patients (triangular face, prominent forehead, large eyes, protruding ears). Despite markedly elevated renin and aldosterone levels, blood pressure is normal or low (distinguishing from conditions with hyperaldosteronism and hypertension). | Kidneys (thick ascending limb of Henle; collecting duct secondary effects; nephrocalcinosis in types 1-2); inner ear (sensorineural hearing loss in type 4); bones (growth retardation); muscles (hypokalemic weakness) | Diagnosis is based on the characteristic biochemical pattern: hypokalemia, metabolic alkalosis, hyperreninemia, hyperaldosteronism, normotension or hypotension, and elevated urinary chloride (>20 mEq/L, distinguishing from vomiting or laxative abuse). Urine calcium is elevated in types 1 and 2 (urine Ca/Cr ratio >0.2 mg/mg) but may be normal in type 3. Serum magnesium is typically normal (distinguishing from Gitelman syndrome where it is low). Renal ultrasound may show nephrocalcinosis in types 1 and 2. Prenatal diagnosis is suggested by polyhydramnios with elevated amniotic fluid chloride. Genetic testing confirms the specific type and is recommended for definitive diagnosis and genetic counseling. Plasma renin activity and aldosterone levels are markedly elevated. Prostaglandin E2 levels are elevated in urine. Differential diagnosis includes diuretic abuse (check urine diuretic screen), chronic vomiting (urine chloride <20 mEq/L), and Gitelman syndrome. | Indomethacin (1-3 mg/kg/day in 2-3 divided doses) is the cornerstone of therapy, reducing prostaglandin E2-mediated renal salt wasting and improving growth; it is effective in all types but particularly in neonatal Bartter syndrome. COX-2 selective inhibitors (celecoxib 3-6 mg/kg/day) may be used as alternatives with potentially fewer GI side effects. Potassium supplementation (potassium chloride 1-3 mEq/kg/day) is essential to correct hypokalemia. Potassium-sparing diuretics (spironolactone 1-3 mg/kg/day or amiloride 0.3-0.5 mg/kg/day) reduce renal potassium losses. ACE inhibitors (enalapril 0.1-0.5 mg/kg/day) may be added to reduce aldosterone-driven potassium wasting. Magnesium supplementation if hypomagnesemia is present. High sodium and potassium diet. Adequate fluid intake to replace urinary losses. Growth hormone therapy may be considered for persistent short stature despite optimized medical management. Hearing aids or cochlear implants for type 4 hearing loss. Renal transplantation is rarely needed as Bartter syndrome does not typically progress to ESRD. | Good - With appropriate treatment, the prognosis is generally good. Growth retardation is correctable with indomethacin and adequate electrolyte supplementation. Neonatal Bartter syndrome (types 1, 2) has the highest early morbidity due to severe salt wasting, but outcomes have improved significantly with modern neonatal care. Long-term renal function is generally well preserved, and progression to ESRD is uncommon (<5%) unless complicated by severe nephrocalcinosis. Nephrocalcinosis from hypercalciuria may cause progressive CKD in some patients. Intellectual development is generally normal with appropriate treatment. Sensorineural hearing loss in type 4 is progressive and requires auditory rehabilitation. Lifelong treatment and monitoring are required. Overall life expectancy is near normal with appropriate management. | E26.81 |
| 25 | 23 | Chronic Interstitial Nephritis | Tubular & Interstitial Diseases | Chronic interstitial nephritis (CIN) represents the end result of prolonged or recurrent injury to the renal tubulointerstitium from diverse etiologies, characterized by interstitial fibrosis, tubular atrophy, and chronic inflammatory cell infiltrate. Unlike AIN, CIN develops insidiously over months to years and is often irreversible by the time of diagnosis. Causes include chronic drug exposure (analgesics, lithium, calcineurin inhibitors, aristolochic acid), chronic obstruction, chronic reflux, recurrent pyelonephritis, heavy metals (lead, cadmium), metabolic disorders (hyperuricemia, hypercalcemia, hypokalemia, oxalosis), autoimmune diseases (Sjogren syndrome, SLE, sarcoidosis, IgG4-related disease), hematologic diseases (sickle cell disease, multiple myeloma), and radiation. The pathogenesis involves sustained tubular injury leading to epithelial-mesenchymal transition (tubular cells differentiate into myofibroblasts), activation of interstitial fibroblasts, excessive extracellular matrix deposition (collagen I, III, fibronectin), and progressive replacement of functional nephrons with fibrotic tissue. The interstitial inflammatory infiltrate is predominantly mononuclear (lymphocytes, macrophages) with profibrotic cytokine production (TGF-beta, CTGF, PDGF). Tubular atrophy leads to loss of concentrating ability, acidification defects, and sodium wasting before significant GFR decline occurs. | CIN accounts for approximately 10-15% of CKD cases and 5-10% of ESRD in developed countries. The true prevalence is difficult to determine because CIN is often a histologic diagnosis and many patients are not biopsied. Analgesic nephropathy was historically the most common cause (responsible for up to 15-20% of ESRD in Australia, Belgium, and Switzerland before analgesic restrictions), but has declined significantly with regulation of phenacetin-containing compounds. Lithium nephropathy affects 15-20% of patients on long-term lithium therapy. Calcineurin inhibitor nephrotoxicity is a major cause of chronic allograft dysfunction in transplant recipients. | CIN can occur at any age depending on the underlying cause. Analgesic nephropathy typically presents in the fifth to sixth decade after decades of analgesic abuse. Lithium nephropathy develops after years of therapy, typically presenting after 10-20 years of use. Lead nephropathy may present in adulthood after chronic occupational or environmental exposure. Sjogren syndrome-associated CIN presents in middle-aged women. Balkan endemic nephropathy affects adults in their 30s-50s. Reflux-associated CIN may present in childhood or early adulthood. | CIN typically presents insidiously with gradually declining renal function. Polyuria, nocturia, and polydipsia from impaired concentrating ability are early symptoms, often preceding significant GFR decline. Mild proteinuria (usually <1-2 g/day, predominantly tubular proteins such as beta-2 microglobulin) is typical; nephrotic-range proteinuria is unusual and suggests concurrent glomerular disease. Hyperchloremic metabolic acidosis from impaired tubular acid excretion (renal tubular acidosis type 1 or 4) is common. Salt-wasting nephropathy may cause orthostatic hypotension. Anemia may be disproportionate to the degree of renal impairment due to impaired erythropoietin production from the damaged interstitium. Hypertension develops as CKD progresses. Electrolyte abnormalities (hyperkalemia, hypophosphatemia, hypomagnesemia) depend on the specific tubular segments affected. Symptoms of the underlying disease may be present. | Kidneys (tubulointerstitium - fibrosis and tubular atrophy); may affect multiple organs depending on underlying cause (joints in sarcoidosis, eyes and salivary glands in Sjogren syndrome, multiple organs in IgG4-RD) | CIN is often a diagnosis of exclusion or biopsy-confirmed finding. Renal biopsy shows interstitial fibrosis, tubular atrophy with thickened tubular basement membranes, chronic inflammatory cell infiltrate (lymphocytes, macrophages), and relative sparing of glomeruli (which may show secondary ischemic changes). Urinalysis shows bland sediment with minimal proteinuria (usually <1 g/day) and tubular proteinuria pattern (elevated beta-2 microglobulin or alpha-1 microglobulin). Renal ultrasound shows small kidneys with increased cortical echogenicity and loss of corticomedullary differentiation in advanced disease. Impaired urinary concentrating ability (low urine osmolality after water deprivation) is an early finding. Renal tubular acidosis may be detected by arterial blood gas and urine pH studies. Investigation for underlying cause includes medication history (analgesics, lithium, NSAIDs), heavy metal levels (blood lead, urine cadmium), autoimmune serologies (ANA, anti-SSA/SSB, serum IgG4), uric acid levels, and imaging for obstruction. | Treatment is directed at the underlying cause. Cessation of the offending agent (analgesics, lithium, nephrotoxic drugs) is essential and may stabilize or slow progression. ACE inhibitors or ARBs for blood pressure control and antiproteinuric effect (ramipril 2.5-10 mg daily or losartan 50-100 mg daily), targeting BP <130/80 mmHg. Correction of metabolic abnormalities: sodium bicarbonate (650 mg-1.3 g two to three times daily) for metabolic acidosis, potassium supplementation or restriction as needed, and phosphate management. Corticosteroids (prednisone 0.5-1 mg/kg/day) for autoimmune causes (sarcoidosis, Sjogren, IgG4-related disease). Chelation therapy (EDTA, succimer) for lead nephropathy. Allopurinol (100-300 mg daily) for hyperuricemic nephropathy. General CKD management including erythropoiesis-stimulating agents for anemia, vitamin D supplementation, dietary modification, and avoidance of nephrotoxins. Renal replacement therapy for ESRD. | Variable - Prognosis depends on the underlying cause, duration of exposure, and extent of fibrosis at diagnosis. Early recognition and removal of the offending agent may stabilize or slow progression. Established fibrosis is generally irreversible. Analgesic nephropathy may stabilize or improve slowly after cessation of analgesics, but many patients have already developed advanced CKD. Lithium nephropathy may continue to progress even after lithium discontinuation in patients with established fibrosis. Sjogren and sarcoidosis-associated CIN may respond to corticosteroids if diagnosed early, before extensive fibrosis. Overall, CIN progresses to ESRD in 30-50% of patients over 5-10 years depending on the underlying cause. The rate of GFR decline is typically 2-5 mL/min/year in untreated progressive CIN. | N11.9 |
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