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?

Question

Accepted Answer

A. Subepithelial immune complex deposits on electron microscopy. ## 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).

Answer

B. Positive anti-GBM antibodies (linear IgG deposits on immunofluorescence)

Answer

C. Rapid decline in GFR over days to weeks

Answer

D. Crescentic glomerulonephritis on kidney biopsy

Explanation

Rapidly Progressive Glomerulonephritis (RPGN) and Pulmonary Hemorrhage

Pathology of RPGN

Histology

Immunofluorescence Patterns in RPGN

Electron Microscopy in RPGN

Clinical Features of RPGN

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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)