A 35-year-old woman from Delhi presents with progressive dyspnea, hemoptysis, and hematuria over 2 weeks. Chest X-ray shows bilateral alveolar infiltrates. Serum creatinine is 3.8 mg/dL. Urinalysis shows RBC casts and dysmorphic RBCs. Anti-GBM (anti-basement membrane) antibodies are positive. Kidney biopsy shows linear IgG deposition along the GBM on immunofluorescence. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Goodpasture Syndrome (Anti-GBM Disease) ### Defining Features **Key Point:** Goodpasture syndrome is a rare, rapidly progressive autoimmune disease characterized by circulating anti-GBM antibodies targeting the NC1 domain of type IV collagen, causing simultaneous pulmonary hemorrhage and rapidly progressive glomerulonephritis (RPGN). ### Pathognomonic Findings | Feature | Goodpasture | GPA | MPA | SLE | |---------|-------------|-----|-----|-----| | **Anti-GBM antibodies** | ✓ (diagnostic) | ✗ | ✗ | ✗ | | **Linear IgG on IF** | ✓ (pathognomonic) | Segmental necrotizing | Segmental necrotizing | Granular IgG/IgA/IgM | | **Pulmonary hemorrhage** | ✓ (common) | ✓ (less common) | ✓ (less common) | ✓ (rare) | | **ANCA status** | Negative | c-ANCA/PR3+ | p-ANCA/MPO+ | Negative (ANA+) | | **GBM necrosis** | Crescentic | Crescentic | Crescentic | Wire-loop lesions | | **Prognosis** | Poor (RPGN) | Variable | Variable | Better with treatment | ### Pathophysiology 1. **Autoimmune attack on basement membrane:** Anti-GBM IgG antibodies bind to the α3 chain of type IV collagen in the GBM and alveolar basement membrane (ABM). 2. **Complement activation:** Binding triggers classical complement activation → C3/C5 deposition → neutrophil recruitment → crescentic GN. 3. **Linear pattern:** Unlike immune complex deposition (granular), anti-GBM produces a continuous linear pattern of IgG along the entire GBM on immunofluorescence. **High-Yield:** **Linear IgG + anti-GBM antibodies + pulmonary hemorrhage + RPGN = Goodpasture syndrome.** ### Clinical Presentation **Mnemonic: RPGN + PULMONARY = Goodpasture** - **R**apidly **P**rogressive **G**lomerulonephritis - **P**ulmonary hemorrhage (hemoptysis, dyspnea, bilateral infiltrates) - **U**remia (rising creatinine, oliguria) - **L**inear IgG on immunofluorescence - **M**ay present with renal-only disease (10–15% of cases) - **O**nset typically in 20–40 years - **N**egative ANCA (distinguishes from vasculitis) - **A**nti-GBM antibodies in serum - **R**apid decline in renal function (days to weeks) - **Y**oung to middle-aged patients ### Clinical Pearl **Clinical Pearl:** Goodpasture is a medical emergency. Without treatment, it progresses to end-stage renal disease (ESRD) within weeks and is fatal if pulmonary hemorrhage is severe. Immediate plasmapheresis + immunosuppression (corticosteroids + cyclophosphamide) is life-saving. ### Management Algorithm ```mermaid flowchart TD A[Suspected Goodpasture]:::outcome --> B[Anti-GBM serology]:::decision B -->|Positive| C[Confirm with kidney biopsy]:::action C --> D[Linear IgG on IF?]:::decision D -->|Yes| E[RPGN confirmed]:::outcome E --> F[Start plasmapheresis immediately]:::urgent F --> G[Add IV methylprednisolone]:::action G --> H[Add cyclophosphamide]:::action H --> I[Monitor renal function & hemoglobin]:::action B -->|Negative| J[Consider ANCA-associated vasculitis or other RPGN]:::outcome ``` ### Prognosis - **With treatment:** ~80% achieve remission if caught early (Cr <5 mg/dL). - **Without treatment:** Nearly 100% progress to ESRD; mortality from pulmonary hemorrhage is high. - **Renal recovery:** Rare if dialysis-dependent at presentation.