A 35-year-old woman with a 3-week history of productive cough and hemoptysis is found to have hematuria, proteinuria, and dysmorphic RBC casts on urinalysis. Chest X-ray shows bilateral alveolar infiltrates. Serum creatinine is elevated. Which of the following is NOT a characteristic finding in rapidly progressive glomerulonephritis (RPGN) associated with pulmonary hemorrhage?

Explanation

## Rapidly Progressive Glomerulonephritis (RPGN) and Pulmonary Hemorrhage **Key Point:** RPGN is characterized by **crescent formation** and rapid renal deterioration. When combined with pulmonary hemorrhage, the classic diagnosis is anti-GBM disease (Goodpasture syndrome) or ANCA-associated vasculitis. ### Pathology of RPGN #### Histology - **Crescentic GN** — defining feature - Extracapillary proliferation of parietal epithelial cells - Fibrin deposition - Rapid glomerular destruction - Endocapillary proliferation may be absent or minimal - Necrosis of the glomerular tuft #### Immunofluorescence Patterns in RPGN | Type | IF Pattern | Clinical Association | | --- | --- | --- | | **Anti-GBM disease** | Linear IgG along GBM | Pulmonary hemorrhage (Goodpasture) | | **ANCA-associated** | Pauci-immune (minimal/no deposits) | Granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) | | **Immune complex** | Granular deposits (IgG/IgM/C3) | Lupus, post-infectious GN (rare in RPGN) | **High-Yield:** Anti-GBM disease presents with the **pulmonary-renal syndrome**: hemoptysis + hematuria + rapidly rising creatinine. Linear IgG on IF is diagnostic. ### Electron Microscopy in RPGN - **Pauci-immune RPGN** (ANCA-associated): minimal or no electron-dense deposits - **Anti-GBM disease**: **NO subepithelial immune complex deposits** — the disease is mediated by antibodies to the GBM itself, not immune complexes - **Immune complex RPGN** (rare): granular deposits present, but RPGN is uncommon in this category **Clinical Pearl:** Subepithelial humps are characteristic of post-streptococcal GN, NOT RPGN. RPGN is typically pauci-immune or anti-GBM, neither of which shows subepithelial deposits. ### Clinical Features of RPGN 1. **Rapid GFR decline** — creatinine may double in days to weeks 2. **Nephritic presentation** — hematuria, RBC casts, hypertension 3. **Pulmonary involvement** (in anti-GBM and some ANCA cases) — hemoptysis, infiltrates 4. **Systemic symptoms** — fever, malaise, arthralgia (especially in ANCA-associated) **Mnemonic for RPGN causes:** **ANCA** = Anti-Neutrophil Cytoplasmic Antibody (GPA, MPA, EGPA); **Anti-GBM** = Goodpasture; **IC** = Immune Complex (rare in RPGN, e.g., lupus with severe proliferation).