A 42-year-old woman from Mumbai presents with a 6-week history of fever, arthralgia, and a palpable purpura rash on the lower extremities and buttocks. Urinalysis shows hematuria and mild proteinuria. Serum creatinine is 1.2 mg/dL. Skin biopsy shows IgA-dominant immune complex deposition. What is the most appropriate next step in management?

Explanation

## Clinical Diagnosis: IgA Vasculitis (IgAV, formerly IgA Nephropathy Vasculitis) The presentation is classic: palpable purpura (lower extremities and buttocks), arthralgia, hematuria with proteinuria, and IgA-dominant immune complex deposition on skin biopsy. ## Management Strategy: Risk Stratification via Renal Biopsy **Key Point:** IgA vasculitis has variable renal involvement (from asymptomatic hematuria to rapidly progressive glomerulonephritis). Renal biopsy is essential to determine prognosis and guide intensity of immunosuppressive therapy. **High-Yield:** The presence of hematuria + proteinuria + elevated creatinine (even mild) mandates renal biopsy to assess: - Histological grade (MEST-C score) - Extent of glomerular, interstitial, and vascular involvement - Presence of crescents (indicator of aggressive disease) ### Why Renal Biopsy Is the Next Step 1. **Risk stratification:** MEST-C scoring predicts progression to ESRD - M (mesangial): proliferation grade - E (endocapillary): proliferation - S (segmental): sclerosis - T (tubular): atrophy - C (crescents): percentage 2. **Treatment tailoring:** - **Low-risk disease** (no crescents, minimal proteinuria): supportive care ± corticosteroids - **High-risk disease** (crescents >25%, proteinuria >1 g/day): immunosuppression (corticosteroids + cyclophosphamide or mycophenolate) 3. **Baseline assessment:** Establishes degree of chronicity and reversibility **Clinical Pearl:** In IgAV with renal involvement, the histological findings, not just clinical presentation, determine prognosis. A patient with mild clinical signs may have crescentic disease on biopsy requiring aggressive therapy. ### Management Algorithm Post-Biopsy ```mermaid flowchart TD A[IgA Vasculitis + Hematuria/Proteinuria]:::outcome --> B[Renal Biopsy]:::action B --> C{MEST-C Grade & Crescents?}:::decision C -->|Low-risk: No crescents, proteinuria <1 g/day| D[Supportive care + ACE-I/ARB]:::action C -->|Intermediate: Crescents <25%, proteinuria 1-3 g/day| E[Corticosteroids ± MMF]:::action C -->|High-risk: Crescents >25%, proteinuria >3 g/day| F[Corticosteroids + Cyclophosphamide]:::action D --> G[Monitor renal function & proteinuria]:::action E --> G F --> G ``` **Supportive Measures (All Patients):** - ACE inhibitor or ARB (renoprotective) - Blood pressure control (target <130/80 mmHg) - NSAID use should be minimized (risk of acute kidney injury) - Dietary sodium and protein restriction if proteinuria >1 g/day [cite:Robbins 10e Ch 11; Harrison 21e Ch 319]