Rapidly progressive GN with pulmonary hemorrhage from autoantibodies to the alpha-3 chain of type IV collagen.
Also known as: Goodpasture syndrome, anti-GBM disease, anti-glomerular basement membrane disease, Goodpasture disease, pulmonary-renal syndrome
Overview
An autoimmune small-vessel disease caused by IgG autoantibodies directed against the non-collagenous-1 (NC1) domain of the alpha-3 chain of type IV collagen, found in glomerular and pulmonary alveolar basement membranes. Produces rapidly progressive crescentic glomerulonephritis (RPGN) with or without diffuse alveolar hemorrhage. The term 'Goodpasture syndrome' is used when both kidney and lung are involved; 'anti-GBM disease' may be isolated to the kidney.
Epidemiology
Rare — incidence ~0.5-1 per million per year. Bimodal age distribution with peaks in young adults (20-30, more often with pulmonary involvement) and elderly (60-70, more often kidney-limited). Slight male predominance overall. Strong HLA-DRB1*1501 association.
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Question 1RenalMedium
A 26-year-old man who smokes presents with a 1-week history of hemoptysis followed by dark urine and decreasing urine output. Blood pressure is 158/96 mm Hg and oxygen saturation is 90% on room air. Diffuse inspiratory crackles are heard bilaterally. Serum creatinine is 4.8 mg/dL (baseline normal), and urinalysis shows dysmorphic red blood cells and red blood cell casts. Chest CT shows diffuse bilateral alveolar opacities. A kidney biopsy is performed. Which of the following findings on the biopsy best supports the diagnosis of anti-GBM disease?
ALinear IgG deposition along the glomerular basement membrane
BPauci-immune crescentic glomerulonephritis with scant deposits
CIgA-dominant immune-complex deposits within the mesangium
DGranular immune-complex deposits along glomerular capillary walls
Reveal answer & full explanation
Correct answer: A — Linear IgG deposition along the glomerular basement membrane
ALinear IgG deposition along the glomerular basement membrane✓
BPauci-immune crescentic glomerulonephritis with scant deposits
CIgA-dominant immune-complex deposits within the mesangium
DGranular immune-complex deposits along glomerular capillary walls
Why Linear IgG deposition along the glomerular basement membrane is correct
Anti-GBM disease is driven by IgG autoantibodies against the NC1 domain of the alpha-3 chain of type IV collagen, which binds continuously along the glomerular basement membrane.
On immunofluorescence this produces a smooth, ribbon-like (linear) IgG pattern, often with C3 — the diagnostic hallmark that, combined with crescentic glomerulonephritis on light microscopy, confirms the diagnosis.
The clinical picture (young smoker with alveolar hemorrhage plus rapidly progressive glomerulonephritis) is classic, and a positive serum anti-GBM antibody supports it, but linear IgG on biopsy is the defining finding.
Why the others are wrong
Granular immune-complex deposits along glomerular capillary walls — this is the signature of immune-complex glomerulonephritis such as lupus nephritis (the "full-house" pattern of IgG, IgA, IgM, C3, and C1q); it is granular rather than linear and is accompanied by positive ANA/anti-dsDNA.
Pauci-immune crescentic glomerulonephritis with scant deposits — this is the pattern of ANCA-associated vasculitis (GPA/MPA); both diseases cause rapidly progressive glomerulonephritis, but ANCA vasculitis shows little or no immunofluorescence staining rather than linear IgG. About 30% of anti-GBM patients are also ANCA-positive, so ANCA is always checked.
IgA-dominant immune-complex deposits within the mesangium — this is the finding in IgA nephropathy or IgA vasculitis (Henoch-Schönlein), which presents with hematuria and, in vasculitis, palpable purpura — not alveolar hemorrhage with linear GBM staining.
Question 2RenalMedium
A 26-year-old man who smokes presents with one week of hemoptysis and progressive dyspnea, now with cola-colored urine and ankle swelling. Vitals show BP 162/98 mm Hg and oxygen saturation 90% on room air; exam reveals bilateral inspiratory crackles and conjunctival pallor. Labs show creatinine 4.1 mg/dL, and urinalysis reveals dysmorphic red cells with red-cell casts. Kidney biopsy demonstrates crescentic glomerulonephritis with smooth linear IgG deposition along the glomerular basement membrane on immunofluorescence. Which of the following best explains the findings?
AAutoantibodies against the phospholipase A2 receptor on podocytes
BPauci-immune injury from antineutrophil cytoplasmic antibodies
CGranular subepithelial deposition of circulating immune complexes
DAutoantibodies against the alpha-3 chain of type IV collagen
Reveal answer & full explanation
Correct answer: D — Autoantibodies against the alpha-3 chain of type IV collagen
AAutoantibodies against the phospholipase A2 receptor on podocytes
BPauci-immune injury from antineutrophil cytoplasmic antibodies
CGranular subepithelial deposition of circulating immune complexes
DAutoantibodies against the alpha-3 chain of type IV collagen✓
Why Autoantibodies against the alpha-3 chain of type IV collagen is correct
The clinical picture — young smoker with diffuse alveolar hemorrhage, RPGN, and smooth linear IgG along the GBM — is classic anti-GBM (Goodpasture) disease.
Tolerance is lost to a normally sequestered epitope on the non-collagenous-1 (NC1) domain of the alpha-3 chain of type IV collagen, which is shared by glomerular and alveolar basement membranes.
Circulating IgG binds linearly along these membranes, activates complement, and recruits neutrophils, producing necrotizing-crescentic GN and breakdown of the alveolar-capillary barrier. An environmental hit (smoking, infection, hydrocarbons) is thought to unmask the antigen.
Why the others are wrong
Granular subepithelial deposition of circulating immune complexes — produces a granular ("lumpy-bumpy"), not linear, IF pattern; seen in post-streptococcal GN and membranous nephropathy, not anti-GBM disease.
Pauci-immune injury from antineutrophil cytoplasmic antibodies — ANCA-associated vasculitis (GPA/MPA) also causes crescentic GN and can cause alveolar hemorrhage, but IF shows little or no immune deposits (pauci-immune), not bright linear IgG. About 30% of anti-GBM patients are also ANCA-positive, so ANCA should still be checked.
Autoantibodies against the phospholipase A2 receptor on podocytes — the mechanism of primary membranous nephropathy, which causes nephrotic-range proteinuria with subepithelial deposits, not crescentic GN with pulmonary hemorrhage.
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Lithotripsy or other recent renal injury (rare trigger)
Coexisting ANCA — up to 30% of anti-GBM patients are also ANCA-positive (usually MPO)
Pathophysiology
Loss of tolerance to a hidden epitope on the NC1 domain of the alpha-3 chain of type IV collagen (alpha3(IV)NC1, the 'Goodpasture antigen') leads to circulating IgG anti-GBM antibodies. These bind linearly along glomerular and alveolar basement membranes, activate complement and recruit neutrophils, and cause severe necrotizing-crescentic glomerulonephritis with breakdown of the alveolar-capillary barrier (diffuse alveolar hemorrhage). The autoantigen is normally sequestered; an environmental hit (smoking, infection, hydrocarbons) is thought to unmask it.
Clinical presentation
Symptoms
Hemoptysis (ranging from mild to massive), dyspnea, cough
Definitive diagnosis: kidney biopsy with crescentic glomerulonephritis on LM and linear IgG (and often C3) along the GBM on IF. Serum anti-GBM antibody supports the diagnosis and can be diagnostic when biopsy is contraindicated. Always check ANCA — dual-positive patients have a different prognosis.
Labs
Anti-GBM antibody (ELISA against alpha3 NC1) — high sensitivity and specificity; titer correlates with disease activity
ANCA — MPO and PR3; ~30% of anti-GBM patients are dual-positive
CBC (iron-deficiency anemia from alveolar hemorrhage; sometimes severe)
BMP, eGFR, UA with microscopy (dysmorphic RBCs, RBC casts), spot UPCR
ANA, complement C3/C4 (typically normal), hepatitis serologies, HIV
Arterial blood gas (hypoxemia)
Imaging
Chest X-ray and CT — diffuse bilateral alveolar opacities consistent with alveolar hemorrhage
Renal ultrasound — typically normal-sized kidneys
Bronchoscopy with bronchoalveolar lavage — progressively bloodier returns and hemosiderin-laden macrophages confirm alveolar hemorrhage
Diagnostic algorithm
Pulmonary-renal syndrome
Antibodies
IF pattern
Distinguishing features
Anti-GBM disease
Anti-GBM IgG
Linear IgG along GBM
Young smoker, alveolar hemorrhage, isolated alpha-3(IV) target
Pulmonary-renal syndromes — distinguished by serology and immunofluorescence.
Treatment
First-line
Plasmapheresis daily (or every other day) until anti-GBM antibody becomes undetectable — typically 14 days or longer
Corticosteroids — IV methylprednisolone pulse 500-1000 mg daily × 3 days, then oral prednisone 1 mg/kg/day tapered over 6 months
Cyclophosphamide — oral 2 mg/kg/day or IV pulse, continued for 3 months then transition to maintenance
Supportive care: airway protection, mechanical ventilation for severe alveolar hemorrhage, RBC transfusion, renal replacement therapy if needed
Smoking cessation is mandatory and reduces relapse risk substantially
Anti-GBM only (no ANCA)
Triple therapy (plasmapheresis + steroids + cyclophosphamide) as above
Discontinue immunosuppression at ~6 months — relapse after antibody clearance is rare
Patients dialysis-dependent on presentation without pulmonary hemorrhage and >85% crescents on biopsy may not benefit from aggressive immunosuppression — individualize
Dual anti-GBM + ANCA positive
Treat as severe AAV with longer-term immunosuppression — induction with cyclophosphamide or rituximab + plasmapheresis + steroids
Maintenance with rituximab or azathioprine for ≥18 months because of higher relapse risk
Higher overall relapse rate than anti-GBM only
Second-line / adjunct
Rituximab — alternative to cyclophosphamide in selected patients (lower-quality evidence)
Imlifidase — IgG-cleaving endopeptidase used in clinical trials and case series for severe disease
Kidney transplantation — perform when anti-GBM antibody has been undetectable for ≥6 months; recurrence in graft is uncommon
Complications
Death from massive pulmonary hemorrhage (highest early mortality)
Irreversible kidney failure (ESKD in 30-50%, especially if dialysis-dependent on presentation)
Iron-deficiency anemia from chronic alveolar bleeding
Allograft recurrence (rare with proper preoperative antibody clearance)
PANCE pearls
Linear IgG on immunofluorescence is the hallmark — distinct from the granular IF of immune-complex GN and the pauci-immune pattern of ANCA vasculitis.
Smoking is the strongest modifiable risk factor for pulmonary involvement; counsel aggressively.
Always check ANCA — ~30% of anti-GBM patients are dual-positive, with worse prognosis and higher relapse.
Dialysis-dependent patients without pulmonary hemorrhage and >85% crescents may not recover renal function — individualize aggressive therapy in this group.
Plasmapheresis must continue until anti-GBM antibody is undetectable, not just for a fixed number of sessions.
References
KDIGO 2021 — KDIGO 2021 Clinical Practice Guideline for the Management of Glomerular Diseases (Kidney Int 2021;100:S1-S276)
Chapel Hill 2012 — Jennette JC et al. 2012 Revised International Chapel Hill Consensus Conference Nomenclature of Vasculitides (Arthritis Rheum 2013;65:1-11)
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