A 28-year-old Indian man with a 10-year history of systemic lupus erythematosus (SLE) presents with nephrotic-range proteinuria (5.2 g/24 h), serum albumin 2.3 g/dL, and total cholesterol 280 mg/dL. Serum creatinine is 1.8 mg/dL (baseline 0.9 mg/dL). Urinalysis shows 4+ proteinuria with RBC casts and dysmorphic RBCs. Renal biopsy shows diffuse proliferative glomerulonephritis with subendothelial and subepithelial immune complex deposits. Which of the following best describes the WHO/ISN-RPS lupus nephritis class?

Explanation

## Diagnosis: WHO/ISN-RPS Class IV Lupus Nephritis (Diffuse Proliferative) ### WHO/ISN-RPS Classification of Lupus Nephritis | Class | Histology | Proteinuria | Hematuria | Renal Function | Prognosis | | --- | --- | --- | --- | --- | --- | | I (minimal) | Normal or near-normal | <0.5 g/day | Absent | Normal | Excellent | | II (mesangial) | Mesangial proliferation only | Variable | Mild | Normal | Good | | III (focal proliferative) | <50% glomeruli involved | Variable | Present | Mild ↑Cr | Intermediate | | IV (diffuse proliferative) | ≥50% glomeruli involved | Nephrotic range | RBC casts, dysmorphic RBCs | ↑Cr (often significant) | Poorest | | V (membranous) | Capillary wall thickening ± proliferation | Nephrotic range | Absent/mild | Normal/mild ↑ | Intermediate | | VI (advanced sclerosing) | >90% sclerosed glomeruli | Variable | Absent | ESRD | ESRD | **Key Point:** Class IV is the most severe form and represents the worst prognosis among lupus nephritis classes. It is defined by involvement of ≥50% of glomeruli with proliferative changes. ### Clinical Features of Class IV in This Case 1. **Nephrotic-range proteinuria** (5.2 g/24 h) — hallmark of diffuse disease 2. **RBC casts and dysmorphic RBCs** — indicate active proliferative glomerulonephritis 3. **Rising serum creatinine** (1.8 from baseline 0.9) — sign of significant renal involvement 4. **Diffuse proliferative changes** on biopsy — ≥50% glomeruli affected 5. **Both subendothelial AND subepithelial deposits** — "full house" pattern typical of SLE ### Electron Microscopy Pattern: "Full House" **High-Yield:** SLE shows IgG, IgA, IgM, C1q, and C3 deposits in multiple compartments (subendothelial, subepithelial, mesangial, intramembranous). This "full house" pattern is virtually pathognomonic for lupus nephritis. ### Subclassification of Class IV - **IV-S (segmental):** <50% of glomerular tuft involved - **IV-G (global):** ≥50% of glomerular tuft involved (this patient) **Clinical Pearl:** Class IV lupus nephritis requires aggressive immunosuppression (corticosteroids + cyclophosphamide or mycophenolate mofetil) to prevent progression to ESRD. ### Prognosis and Management **Mnemonic:** **DIFFUSE = DANGEROUS** — Class IV requires the most intensive therapy to prevent renal failure. ```mermaid flowchart TD A[Lupus Nephritis Biopsy]:::outcome --> B{Glomerular involvement?}:::decision B -->|Mesangial only| C[Class II]:::outcome B -->|Proliferative changes| D{Extent of involvement?}:::decision D -->|Less than 50%| E[Class III - Focal]:::outcome D -->|50% or more| F[Class IV - Diffuse]:::urgent F --> G{Subepithelial deposits?}:::decision G -->|Yes, both subendo + subepi| H[Full House Pattern]:::outcome H --> I[Aggressive immunosuppression]:::action ```