Rapidly Progressive Glomerulonephritis (RPGN)
RPGN is a clinical syndrome characterized by a rapid decline in GFR (usually 50% or more over a few weeks or months). It is a medical emergency that can progress to end-stage renal disease (ESRD) within weeks if left untreated.
1. Hallmark Histology: The Crescent
The defining feature of all RPGN types is the formation of crescents in Bowman’s space. These are composed of fibrin, plasma proteins, and proliferating parietal epithelial cells/macrophages.
2. Classification by IF Findings
| Type | IF Pattern | Associated Conditions |
|---|---|---|
| Type I | Linear | Goodpasture Syndrome (anti-GBM antibodies). |
| Type II | Granular | PSGN, SLE, IgA nephropathy. |
| Type III | Pauci-immune | ANCA-associated vasculitides (e.g., GPA/Wegener’s, MPA). |
3. Exam Must-Knows
- Goodpasture Syndrome: Specifically affects the lungs and kidneys (hemoptysis + hematuria). Pathophysiology involves antibodies against the alpha-3 chain of collagen type IV.
- ANCA Testing: Essential in Pauci-immune types (Type III). c-ANCA (PR3) vs. p-ANCA (MPO).
- Clinical Urgency: Requires aggressive treatment with corticosteroids and cyclophosphamide (or other immunosuppressants), often combined with plasmapheresis for Type I.
Pathology Board Hint: For board vignettes, if you see a patient with rapid renal decline and the word “crescent” in the biopsy description, you are looking at RPGN. If the patient *also* has lung involvement, it’s almost certainly Goodpasture syndrome (Type I).