A 28-year-old woman with biopsy-proven lupus nephritis (Class IV, diffuse proliferative) presents with proteinuria 3.5 g/day, serum creatinine 1.8 mg/dL, and active urinary sediment. She is currently on prednisolone 1 mg/kg/day. Complement levels (C3, C4) are low, and anti-dsDNA titres are elevated. What is the most appropriate next step in management?

Explanation

## Management of Class IV Lupus Nephritis **Key Point:** Class IV (diffuse proliferative) lupus nephritis is the most severe form and requires aggressive combination immunosuppression — corticosteroids PLUS a cytotoxic agent (cyclophosphamide or MMF) — to prevent progression to end-stage renal disease. ### Rationale for Induction Therapy This patient has: - Active proliferative nephritis (Class IV) - Significant proteinuria (3.5 g/day) and renal impairment (Cr 1.8) - Active serology (low complement, high anti-dsDNA) - Already on adequate-dose corticosteroids **High-Yield:** Corticosteroids alone are insufficient for Class IV disease. The standard induction regimen is: 1. **Cyclophosphamide:** 500–1000 mg/m² IV monthly × 6 months (NIH protocol), OR 2. **Mycophenolate mofetil (MMF):** 1–3 g/day (Euro-Lupus protocol) Both are superior to prednisolone monotherapy in preventing progression to ESRD [cite:Harrison 21e Ch 319]. ### Why Cyclophosphamide or MMF? | Agent | Mechanism | Indication | Advantage | Disadvantage | |-------|-----------|-----------|-----------|---------------| | **Cyclophosphamide** | Alkylating agent; cross-links DNA | Class III–IV nephritis | Faster remission; proven long-term renal preservation | Infertility, infection risk, hemorrhagic cystitis | | **MMF** | Inosine monophosphate dehydrogenase inhibitor; selective T/B cell suppression | Class III–IV nephritis | Better tolerability; less gonadotoxicity | Slower onset; GI side effects | | **Azathioprine** | 6-mercaptopurine analogue | Maintenance only, not induction | Low toxicity | Insufficient for active proliferative disease | **Clinical Pearl:** MMF is increasingly preferred in young women of childbearing age due to lower gonadotoxicity; cyclophosphamide remains gold standard in severe/rapidly progressive disease. ### Treatment Algorithm ```mermaid flowchart TD A[Lupus nephritis diagnosed]:::outcome --> B{Class?}:::decision B -->|Class I-II| C[Prednisolone ± hydroxychloroquine]:::action B -->|Class III-IV| D[Prednisolone + cytotoxic agent]:::action D --> E{Agent choice?}:::decision E -->|Severe/rapid progression| F[Cyclophosphamide IV]:::action E -->|Mild-moderate/young woman| G[MMF 1-3 g/day]:::action F --> H[Induction 6 months]:::action G --> H H --> I[Maintenance: azathioprine or MMF]:::action I --> J[Monitor Cr, proteinuria, serology]:::outcome ``` **Mnemonic:** **CIMM** — **C**yclophosphamide or **I**nduction, **M**ycophenolate **M**ofetil (for Class III–IV lupus nephritis). ## Why Not the Other Options? - **Prednisolone monotherapy:** Inadequate for Class IV disease; high relapse and ESRD risk without cytotoxic agent. - **Azathioprine alone:** Maintenance agent only; lacks potency for active induction phase. - **Plasmapheresis:** Not first-line; reserved for severe vasculitis, thrombotic microangiopathy, or rapidly progressive renal failure unresponsive to immunosuppression.