A 35-year-old man presents with palpable purpura on the lower limbs. Biopsy shows fibrinoid necrosis of vessel walls with neutrophilic infiltrate and leucocytoclasia (nuclear dust) involving small vessels in the superficial dermis. Direct immunofluorescence shows IgA deposition in vessel walls. What is the diagnosis and the underlying mechanism?

• A ANCA-associated vasculitis — PR3-ANCA mediated
• B Cryoglobulinaemic vasculitis — mixed cryoglobulins
• C IgA vasculitis (Henoch-Schönlein Purpura) — IgA1 immune complex deposition activating complement ✓
• D Urticarial vasculitis — anti-C1q antibodies

Explanation

IgA vasculitis (formerly Henoch-Schönlein Purpura) is a small-vessel vasculitis defined by IgA1 immune complex deposition in vessel walls — this is its defining criterion on DIF. The IgA complexes (aberrantly glycosylated IgA1) activate the lectin complement pathway, causing endothelial damage and neutrophilic infiltration (leukocytoclastic vasculitis on histology). The classic tetrad includes palpable purpura, arthritis, abdominal pain, and renal involvement. DIF showing IgA in vessel walls is pathognomonic and distinguishes it from other small-vessel vasculitides.

Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.