Types and Diagnosis of Glomerulonephritis

Classification and Diagnosis of Glomerulonephritis Introduction Glomerulonephritis represents a spectrum of kidney diseases affecting the glomeruli, the filtering units of the kidney. Understanding these diseases requires learning to classify them by their histological appearance under the microscope, their clinical presentation, and their underlying mechanisms. This classification directly guides diagnosis, treatment, and prognosis. The classification system divides glomerulonephritis into two major categories based on what you see under the microscope: non-proliferative forms (no increase in cell numbers) and proliferative forms (increased cell numbers). Importantly, these categories correlate with different clinical presentations—non-proliferative diseases typically cause nephrotic syndrome, while proliferative diseases typically cause nephritic syndrome. Understanding this relationship is crucial for recognizing patterns in patient presentations. Non-Proliferative Glomerulonephritis Non-proliferative glomerulonephritis is characterized by the absence of increased cellularity in the glomeruli. On light microscopy (the standard microscope examination), these diseases appear relatively normal, yet they cause significant protein loss. Patients with non-proliferative GN typically present with nephrotic syndrome—meaning heavy proteinuria (>3.5 g/day), hypoalbuminemia, edema, and hyperlipidemia. The key feature across these diseases is that the damage occurs at the podocyte level (the cells that form the filtration barrier) rather than in the glomerular structure itself, which is why light microscopy appears normal. Electron microscopy, a more powerful magnification technique, is often needed to see the actual damage. Minimal Change Disease Minimal change disease (MCD) is the most common cause of nephrotic syndrome in children, accounting for about 85-90% of cases in this age group. Despite causing significant proteinuria, its name reflects its appearance: there are minimal or no visible changes on light microscopy. Key diagnostic feature: Electron microscopy reveals fusion of podocyte foot processes—imagine the tiny "feet" that podocytes use to wrap around the glomerular basement membrane (GBM) melting together, creating gaps in the filtration barrier. This damage is specific but invisible on light microscopy. Clinical presentation: Patients present with nephrotic syndrome—heavy proteinuria, hypoalbuminemia, edema, and hyperlipidemia. The disease typically develops acutely. Prognosis and treatment: This is one of the more favorable forms of GN. MCD responds well to corticosteroids, and most patients (>90%) achieve remission. Importantly, minimal change disease typically does not progress to chronic kidney disease if treated appropriately. Renal function usually remains normal. Why this matters for exams: When you see a child with nephrotic syndrome, minimal change disease should be your first thought. It's also important to remember that MCD doesn't cause permanent kidney damage. Focal Segmental Glomerulosclerosis Focal segmental glomerulosclerosis (FSGS) involves sclerosis (scarring) of segments of some glomeruli—hence "focal" (not all glomeruli) and "segmental" (not the entire glomerulus). This represents permanent scarring damage, which is why the prognosis differs from minimal change disease. Light microscopy findings: You can actually see the scarring on regular light microscopy, unlike MCD. Some glomeruli show segmental sclerosis while others appear normal. Clinical presentation: FSGS presents with nephrotic syndrome, though proteinuria may be variable. Associations and causes: FSGS can be: Primary (idiopathic): Occurring without an obvious cause Secondary to systemic conditions: HIV infection, heroin abuse, obesity Genetic: Inherited as part of Alport syndrome (a hereditary condition affecting the basement membrane) Treatment and prognosis: While corticosteroids are used, they are less effective than in minimal change disease. Notably, up to 50% of patients progress to end-stage renal disease (ESRD) requiring dialysis or transplantation. This is a critical prognostic difference compared to MCD. Why this matters for exams: FSGS is important because it looks similar to MCD clinically (both cause nephrotic syndrome), but the prognosis is dramatically different. Understanding the associations with HIV and IV drug use helps with clinical recognition. Membranous Glomerulonephritis Membranous glomerulonephritis is characterized by thickening of the glomerular basement membrane due to immune complex deposition. It's the most common cause of nephrotic syndrome in adults. Light microscopy findings: The GBM appears uniformly thickened—visible on staining with special techniques like periodic acid-Schiff (PAS) stain. Electron microscopy findings: The pathognomonic finding is the "spike and dome" pattern—electron-dense deposits sit on the outer surface of the GBM with spikes of GBM material projecting between them, creating a distinctive appearance. Immunofluorescence findings: Granular IgG deposits are visible along the GBM, reflecting immune complex deposition. Cause and associations: Approximately two-thirds of membranous GN is "primary" (meaning idiopathic, with no identifiable secondary cause). These cases are associated with autoimmune antibodies against phospholipase A₂ receptor (PLA₂R), a podocyte surface protein. Testing for anti-PLA₂R antibodies helps confirm the diagnosis. One-third of cases are "secondary", associated with: Malignancy (especially lung and bowel cancers) Hepatitis B or C infection Malaria Systemic lupus erythematosus (SLE) Medications (penicillamine) This is critical: in adults presenting with membranous GN, especially if secondary associations are present, further workup for underlying cancer is warranted. Clinical presentation: Nephrotic syndrome is typical, often with microscopic or gross hematuria. Prognosis: The "rule of thirds" helps remember outcomes: approximately One-third of patients achieve remission One-third remain stable with persistent proteinuria One-third progress to end-stage renal disease This variable prognosis reflects heterogeneity in disease behavior. Presence of anti-PLA₂R antibodies may help predict progression. Why this matters for exams: Membranous GN is the leading cause of nephrotic syndrome in adults and requires screening for malignancy. The distinctive electron microscopy findings are frequently tested. Thin Basement Membrane Disease Thin basement membrane (TBM) disease is a distinct entity characterized by uniformly thin glomerular basement membranes—less than 250 nm thick on electron microscopy (normal is 300-350 nm). Genetics: This is an autosomal dominant condition, meaning affected individuals have one copy of a mutated gene. Often discovered incidentally on kidney biopsy performed for other reasons. Clinical presentation: Patients have persistent microscopic hematuria (red blood cells visible only under the microscope, not in gross hematuria). Proteinuria is usually mild or absent. Prognosis: This is the most benign form of glomerulonephritis. Renal function is preserved, and there is no progression to kidney disease. Many patients have normal lifespans with only persistent hematuria as a reminder of the diagnosis. Why this matters for exams: TBM disease is important to recognize because it's completely benign—it requires reassurance rather than aggressive treatment. The key distinguishing feature is normal or near-normal renal function with isolated microscopic hematuria. Proliferative Glomerulonephritis Proliferative glomerulonephritis is characterized by increased numbers of cells in the glomerulus—you can actually see more nuclei under the microscope. This cellularity increase represents an active inflammatory process with recruitment of immune cells and glomerular cell proliferation. Patients with proliferative GN typically present with nephritic syndrome, which includes hematuria (often gross, giving urine a cola or smoky-brown color), mild-to-moderate proteinuria, hypertension, and reduced renal function. This contrasts with the heavy proteinuria seen in non-proliferative disease. Important prognosis note: Many proliferative forms carry a worse prognosis than non-proliferative disease, often progressing to chronic kidney disease over weeks to years. IgA Nephropathy (Berger's Disease) IgA nephropathy is the most common type of glomerulonephritis worldwide, accounting for about 10% of all GN cases in developed countries and up to 40% in some Asian countries. Pathophysiology: IgA immune complexes deposit in the glomerular mesangium (the central support structure of the glomerulus). The presence of IgA dominance on immunofluorescence staining is the defining feature. Clinical presentation: Visible (gross) or hidden (microscopic) hematuria is the hallmark—often following a respiratory infection by 1-2 days Low-grade proteinuria is common Renal function may initially be normal or mildly reduced Episodes often recur with subsequent respiratory infections Timing clue: Unlike post-infectious GN (discussed next), which has a 1-4 week delay between infection and kidney disease, hematuria in IgA nephropathy appears within days of a respiratory infection—this is a useful diagnostic distinction. Age and demographics: Most commonly affects young adults, though can occur at any age. Prognosis: Highly variable. Some patients have benign courses with stable renal function, while others progress to ESRD over 10-20 years. Poor prognostic factors include high proteinuria, high creatinine at diagnosis, and hypertension. Why this matters for exams: IgA nephropathy's high prevalence makes it frequently tested. The temporal relationship to respiratory infection and the dominance of IgA on immunofluorescence are key identifying features. Post-Infectious Glomerulonephritis Post-infectious GN (also called post-streptococcal GN when Streptococcus pyogenes is the cause) is an immune complex-mediated disease that typically develops 1-4 weeks after a Streptococcus pyogenes throat infection (compared to IgA nephropathy, which occurs within days). Pathophysiology: Circulating immune complexes (antibody-antigen pairs) deposit in the glomeruli, triggering inflammation and complement activation. Clinical presentation: Smoky-brown or cola-colored urine due to gross hematuria—one of the most characteristic findings Mild-to-moderate proteinuria Low-grade fever and malaise Nausea Mild hypertension (elevated but not severely so) Elevated serum creatinine reflecting reduced renal function Timing: The 1-4 week delay between infection and kidney symptoms is a critical diagnostic clue. Diagnosis: Diagnosis relies on: Clinical presentation and history of recent streptococcal infection Positive antistreptolysin O (ASO) titre—antibodies the body makes against streptococcal antigens, confirming recent infection Low serum complement levels (C3 specifically), reflecting complement consumption Kidney biopsy is rarely needed—the clinical picture is usually diagnostic Histology (if biopsied): Proliferative changes with immune deposits Prognosis: Age-dependent and critical to remember: Children typically recover spontaneously within 1-4 weeks with supportive care alone Adults have a much poorer prognosis, with some progressing to chronic kidney disease or ESRD Why this matters for exams: Post-infectious GN is a classic presentation you need to recognize. The combination of smoky-brown urine, recent throat infection, and low complement is pathognomonic. Understanding that children recover while adults often progress is important for predicting outcomes. Membranoproliferative Glomerulonephritis (MPGN) Membranoproliferative glomerulonephritis combines features of both proliferation (increased cells) and basement membrane alterations. Light microscopy shows increased cellularity in the mesangium and endothelium along with thickening of the glomerular basement membrane. Clinical presentation: Nephritic syndrome with hematuria, proteinuria, hypertension, and reduced renal function. Low complement levels (particularly C3) are characteristic and help differentiate MPGN from other conditions. Prognosis: Generally poor, with many patients progressing toward ESRD. MPGN Type 1 Type 1 MPGN results from immune complex deposition in the mesangium and subendothelial space (underneath the inner lining of the glomerulus). This represents about 80% of MPGN cases. Secondary causes are common and important to identify: Systemic lupus erythematosus Hepatitis B and C infections Chronic infections (bacterial endocarditis, osteomyelitis) MPGN Type 3 Type 3 MPGN involves immune complex deposition in the subepithelial space (underneath the outer layer of the glomerulus)—a rarer variant. <extrainfo> A third type, MPGN Type 2 (also called dense intramembranous deposit disease or DIDD), exists but is beyond typical exam scope. </extrainfo> Why this matters for exams: MPGN's poor prognosis and association with systemic diseases (especially hepatitis C) make it clinically important. Low complement levels are a useful diagnostic clue. Rapidly Progressive Glomerulonephritis (Crescentic GN) Rapidly progressive GN (RPGN) represents a medical emergency with distinctive and aggressive histology. It's characterized by rapid decline in renal function, often progressing from normal kidney function to ESRD within weeks to months. Pathophysiology and histology: The defining feature is crescents—proliferations of parietal epithelial cells (the cells lining Bowman's capsule) in response to fibrin leakage from damaged capillaries into Bowman's space. Monocytes and other inflammatory cells infiltrate. These crescents compress the glomerulus, causing rapid loss of function. RPGN has three distinct types based on immunofluorescence findings, each with different causes and treatment approaches: Type 1: Goodpasture Syndrome Goodpasture syndrome is the rarest form (10% of RPGN cases) but clinically the most distinctive. Pathophysiology: An autoimmune disease where the body produces IgG antibodies against type IV collagen in the glomerular basement membrane. Crucially, these same antibodies also attack the alveolar basement membrane in the lungs, making this a pulmonary-renal syndrome. Clinical presentation: Hemoptysis (coughing up blood from the lungs)—a unique feature distinguishing it from other RPGN types Pulmonary infiltrates on chest X-ray Rapid progression to kidney failure Gross hematuria Immunofluorescence findings: Linear IgG deposits along the GBM—appearing as a continuous line under immunofluorescence, distinguishing this from the granular patterns seen in immune complex disease. This linear pattern reflects the fact that antibodies are binding along the continuous collagen structures of the basement membrane. Serology: Anti-glomerular basement membrane (anti-GBM) antibodies are positive, directly confirming the diagnosis. Treatment: Requires aggressive treatment: High-dose intravenous methylprednisolone (pulse corticosteroids) Cyclophosphamide (an immunosuppressant) Plasmapheresis (removing antibodies from the blood) Without treatment, rapidly progresses to ESRD. Early recognition and aggressive treatment can prevent progression, making this a true medical emergency. Why this matters for exams: Goodpasture syndrome is clinically distinctive (hemoptysis + hematuria) and immediately recognizable with its linear IgG pattern. The combination of pulmonary and renal involvement is pathognomonic. Type 2: Immune-Complex–Mediated RPGN This form represents RPGN secondary to other diseases that produce immune complex deposition. Associations include: Systemic lupus erythematosus Post-infectious GN IgA nephropathy IgA vasculitis Immunofluorescence findings: Granular IgG and complement deposits reflecting immune complex deposition. Clinical presentation and prognosis: Vary depending on the underlying disease but are generally serious. Why this matters for exams: This category captures RPGN that develops in the context of known systemic diseases. Recognition that these diseases can progress to crescentic GN is important. Type 3: Pauci-Immune RPGN Pauci-immune RPGN is associated with antineutrophil cytoplasmic antibody (ANCA)–associated vasculitis—systemic diseases affecting small blood vessels throughout the body. Associated conditions: Granulomatosis with polyangiitis (GPA), formerly called Wegener's granulomatosis—causes necrotizing vasculitis with granulomatous inflammation, often affecting upper and lower respiratory tracts and kidneys Microscopic polyangiitis (MPA)—causes necrotizing vasculitis without granulomas Pathophysiology: Antineutrophil cytoplasmic antibodies (ANCA) activate neutrophils, which then attack blood vessel walls. Why these antibodies develop is not fully understood, but they are highly specific for these diseases. Immunofluorescence findings: The key distinguishing feature is no detectable immune deposits (hence "pauci-immune"—pauci means few). Despite this absence of immune deposits, crescents form and progressive kidney failure develops. This is conceptually different from immune complex-mediated disease where antibody-antigen complexes are deposited in the kidneys. Serology: ANCA testing is positive: c-ANCA (cytoplasmic ANCA) with antibodies to proteinase 3 (PR3)—associated with GPA p-ANCA (perinuclear ANCA) with antibodies to myeloperoxidase (MPO)—associated with MPA Clinical presentation: Systemic symptoms with hematuria, proteinuria, and rapid renal function decline. Pulmonary involvement (hemoptysis) may also occur. Treatment: Similar aggressive approach as Goodpasture: corticosteroids, immunosuppressants (cyclophosphamide), and sometimes plasmapheresis. Why this matters for exams: Pauci-immune RPGN is distinguished from immune complex disease by the absence of immune deposits on staining despite active disease—this is counterintuitive and frequently tested. ANCA positivity is the diagnostic clue. Understanding the distinction between GPA and MPA helps with complete characterization. Diagnosis of Glomerulonephritis Diagnosing glomerulonephritis requires integration of clinical presentation, laboratory abnormalities, and confirmatory testing. Laboratory and Imaging Studies Blood tests serve as important diagnostic tools: Complete blood count: Evaluates for anemia, thrombocytopenia, and white blood cell abnormalities Renal function tests: Serum creatinine and blood urea nitrogen assess renal function and degree of injury Inflammatory markers: ESR and CRP indicate active inflammation Serum complement levels: Low C3 and/or C4 suggest immune complex-mediated disease (post-infectious GN, MPGN, lupus nephritis) Antistreptolysin O (ASO) titre: Confirms recent streptococcal infection, particularly helpful in post-infectious GN Antineutrophil cytoplasmic antibody (ANCA): Positive in ANCA-associated vasculitis (pauci-immune RPGN) Anti-glomerular basement membrane (anti-GBM) antibody: Positive in Goodpasture syndrome Antinuclear antibody (ANA): Screen for systemic lupus erythematosus, particularly when lupus nephritis is suspected Urinalysis and urine microscopy: Hematuria with RBC casts suggests glomerular origin of bleeding (nephritic pattern) Proteinuria quantification helps determine nephrotic vs. nephritic presentation Heavy proteinuria (>3.5 g/day) with fatty casts and lipiduria indicates nephrotic syndrome Renal imaging: Ultrasound is typically normal in acute glomerulonephritis but can show: Enlarged kidneys with increased echogenicity (reflecting edema and inflammation) Preserved corticomedullary differentiation (which is lost in chronic kidney disease) Kidney Biopsy Kidney biopsy is the definitive diagnostic test for glomerulonephritis, providing: Light microscopy: Shows cellularity patterns (proliferative vs. non-proliferative), crescent formation, sclerosis, and basement membrane changes Immunofluorescence microscopy: Reveals immune deposits (IgG, IgA, IgM, complement) and their pattern (linear, granular, absent) Electron microscopy: Demonstrates ultrastructural features—foot process fusion, dense deposits, spike-and-dome pattern, etc. When is biopsy indicated? Biopsy is essential when: Diagnosis is uncertain from clinical and laboratory findings Rapidly progressive renal failure suggests RPGN Clinical presentation doesn't fit typical patterns Secondary glomerulonephritis is suspected and therapy depends on exact diagnosis In some classic presentations (like children with post-infectious GN presenting with smoky urine and low complement), biopsy may be omitted if diagnosis is confident. Summary Table of Key Features To help consolidate learning, here are the critical distinguishing features: Non-proliferative diseases typically present with nephrotic syndrome (heavy proteinuria, edema, hypoalbuminemia) and relatively normal or mildly reduced renal function. Light microscopy is normal or near-normal. Proliferative diseases typically present with nephritic syndrome (hematuria, mild proteinuria, hypertension, renal dysfunction) and show increased cellularity on microscopy. Rapidly progressive GN is a medical emergency characterized by crescents on biopsy and rapid renal function decline. The three types are distinguished by immunofluorescence pattern and serology (linear deposits = Goodpasture; granular deposits = immune complex; no deposits = ANCA-associated). Understanding these patterns—what you see under the microscope, how patients present clinically, and what serological tests are positive—allows systematic approach to diagnosis and prognosis prediction.