A 6-year-old boy develops palpable purpura over the buttocks and lower limbs, colicky abdominal pain, and hematuria. Platelet count is normal. Skin biopsy shows leukocytoclastic vasculitis. Which immunofluorescence finding confirms the diagnosis?

• A Linear deposition of IgG along the glomerular basement membrane
• B Granular mesangial and vascular wall deposition of IgA and C3 ✓
• C Paucity of immunoglobulin staining despite crescent formation
• D Deposition of IgM and complement in a full house pattern

Explanation

IgA vasculitis (Henoch-Schönlein purpura) shows granular IgA, often with C3, deposited in vessel walls and the glomerular mesangium, matching its association with mucosal infections that trigger IgA production. Linear IgG defines anti-GBM disease, a paucity of staining is typical of ANCA-associated vasculitides, and a full-house pattern suggests lupus vasculitis. Normal platelets distinguish it from thrombotic thrombocytopenic purpura.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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