A 58-year-old Indian man presents with a 3-week history of fever, malaise, and progressive dyspnea. On examination, he has a palpable purpura over the lower extremities and buttocks, and his blood pressure is 165/95 mmHg. Laboratory investigations show: hemoglobin 10.2 g/dL, WBC 12,500/μL, creatinine 2.1 mg/dL (baseline 0.9), and urinalysis shows 3+ proteinuria with RBC casts. Chest X-ray reveals bilateral alveolar infiltrates. Skin biopsy shows leukocytoclastic vasculitis with IgA immune complex deposition. What is the most likely diagnosis?

Explanation

## Diagnosis: IgA Vasculitis ### Clinical Presentation The constellation of findings is pathognomonic for IgA vasculitis (formerly Henoch-Schönlein purpura): - **Palpable purpura** over lower extremities and buttocks (classic distribution) - **Glomerulonephritis** (hematuria, RBC casts, proteinuria, elevated creatinine) - **Systemic involvement**: fever, malaise, pulmonary infiltrates - **Leukocytoclastic vasculitis** on skin biopsy ### Pathognomonic Finding **Key Point:** IgA immune complex deposition on immunofluorescence microscopy is the diagnostic hallmark. This distinguishes IgA vasculitis from other small-vessel vasculitides, which typically show ANCA positivity or other immune patterns. ### Pathophysiology **High-Yield:** IgA vasculitis is the most common systemic vasculitis worldwide. It is a small-vessel vasculitis mediated by IgA1-dominant immune complexes affecting skin, joints, GI tract, and kidneys. ### Clinical Features Checklist | Feature | IgA Vasculitis | MPA | GPA | PAN | |---------|---|---|---|---| | Palpable purpura (lower limbs) | ✓ | Rare | Rare | ✗ | | IgA immune deposition | ✓ | ✗ | ✗ | ✗ | | ANCA positivity | ✗ | ✓ (MPO) | ✓ (PR3) | ✗ | | Leukocytoclastic vasculitis | ✓ | ✗ | ✗ | ✗ | | Pulmonary hemorrhage | Possible | Common | Common | ✗ | | Medium-vessel involvement | ✗ | ✗ | ✗ | ✓ | ### Management Approach 1. Confirm diagnosis with skin/kidney biopsy and immunofluorescence 2. Assess renal function and proteinuria severity 3. Initiate corticosteroids (prednisolone 0.5–1 mg/kg/day) for systemic disease 4. Consider immunosuppression (azathioprine, mycophenolate) if severe renal involvement 5. ACE inhibitor/ARB for renal protection **Clinical Pearl:** In children, IgA vasculitis is usually self-limited; in adults, renal involvement is more severe and may progress to chronic kidney disease. [cite:Harrison 21e Ch 319]