In SLE, which of the following renal biopsy findings defines WHO Class IV lupus nephritis and carries the highest risk of progression to end-stage renal disease?

Explanation

## WHO Class IV Lupus Nephritis — Diffuse Proliferative GN **Key Point:** WHO Class IV (diffuse proliferative) lupus nephritis is the most severe form, characterized by endocapillary and/or extracapillary proliferation affecting >50% of glomeruli, with or without crescent formation. It carries the worst renal prognosis. ### WHO Classification of Lupus Nephritis | Class | Histology | Prevalence | Prognosis | 5-Year Renal Survival | | --- | --- | --- | --- | --- | | I | Normal | 5–10% | Excellent | >95% | | II | Mesangial proliferation | 10–15% | Good | >90% | | III | Focal proliferative (<50% glomeruli) | 20–25% | Moderate | 70–80% | | IV | Diffuse proliferative (>50% glomeruli) ± crescents | 40–50% | Poor | 50–70% | | V | Membranous ± proliferation | 10–20% | Variable | 60–80% | | VI | Advanced sclerosis | 5–10% | Very poor | <20% | ### Class IV Features **High-Yield:** Class IV is subdivided into: - **IVa:** Segmental endocapillary proliferation - **IVb:** Global endocapillary proliferation - **IVc:** Segmental extracapillary proliferation (crescents) - **IVd:** Global extracapillary proliferation (crescents) **Clinical Pearl:** Crescent formation (extracapillary proliferation) within Class IV indicates severe, rapidly progressive disease requiring urgent aggressive immunosuppression (induction therapy with cyclophosphamide or mycophenolate mofetil + corticosteroids). ### Pathophysiology 1. Extensive immune complex deposition in glomeruli 2. Complement activation (C1q, C3, C4 deposition on immunofluorescence) 3. Proliferation of endothelial and mesangial cells 4. Crescent formation → glomerular basement membrane rupture 5. Progressive glomerulosclerosis and tubulointerstitial fibrosis **Warning:** Class IV with crescents can progress to ESRD in months to years if not treated aggressively; untreated, ~50% reach ESRD within 5 years. **Mnemonic:** **Class IV = "Diffuse" = Danger** — think of it as the most aggressive, widespread form requiring the most intensive treatment.