A 58-year-old man from rural Maharashtra presents with a 3-week history of fever, malaise, and progressive dyspnea. On examination, he has a blood pressure of 165/95 mmHg, bilateral lower limb edema, and palpable purpura over the lower extremities and buttocks. Laboratory investigations show elevated ESR (95 mm/h), CRP 12 mg/dL, serum creatinine 2.8 mg/dL, and urinalysis reveals hematuria with RBC casts. Chest X-ray shows bilateral hilar infiltrates. Skin biopsy demonstrates leukocytoclastic vasculitis with IgA deposition on immunofluorescence. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: IgA Vasculitis ### Key Clinical Features **Key Point:** IgA vasculitis (formerly Henoch-Schönlein purpura) is the most common systemic vasculitis in children and young adults, characterized by IgA immune complex deposition in small vessels. This patient presents with the classic tetrad: 1. **Palpable purpura** — lower extremities and buttocks (pathognomonic distribution) 2. **Glomerulonephritis** — hematuria with RBC casts, elevated creatinine 3. **Systemic symptoms** — fever, malaise, dyspnea 4. **Skin biopsy confirmation** — leukocytoclastic vasculitis with **IgA deposition** on immunofluorescence (gold standard) ### Pathophysiology **High-Yield:** IgA vasculitis is a small-vessel vasculitis mediated by IgA1-dominant immune complexes. The IgA deposition is the defining pathologic feature and distinguishes it from other small-vessel vasculitides. ### Immunofluorescence Pattern | Vasculitis Type | Immunofluorescence Pattern | Vessel Size | |---|---|---| | IgA vasculitis | **IgA dominant** | Small | | Microscopic polyangiitis | ANCA (MPO or PR3) | Small | | GPA | ANCA (PR3) + granulomas | Small–medium | | PAN | Negative IF | Medium | ### Clinical Pearl **Clinical Pearl:** The **buttock and lower extremity purpura** in a patient with concurrent glomerulonephritis and leukocytoclastic vasculitis is virtually pathognomonic for IgA vasculitis. The presence of IgA deposition on skin biopsy confirms the diagnosis. ### Differential Consideration **Warning:** Do not confuse with microscopic polyangiitis (which has ANCA positivity, no IgA deposition, and typically spares the skin) or GPA (which has granulomas and upper respiratory involvement).