A 34-year-old man reports recurrent burning red plaques on his trunk that last about 36 hours before fading, leaving bruise-like discoloration. Individual lesions do not blanch fully on diascopy. Which single investigation best confirms the suspected diagnosis?

• A Autologous serum skin test
• B Skin biopsy showing leukocytoclastic vasculitis ✓
• C Ice cube test on forearm
• D Firm stroking of the skin (dermographic test)

Explanation

Lesions lasting longer than 24 hours, pain rather than itch, residual purpura or hyperpigmentation, and incomplete blanching point to urticarial vasculitis rather than ordinary urticaria. The diagnosis is confirmed by skin biopsy demonstrating leukocytoclastic venulitis. Complement levels should also be checked because the hypocomplementaemic variant carries systemic risk. Autologous serum testing applies to chronic spontaneous urticaria, and the other two tests diagnose physical urticarias.

Reference: Rook's Textbook of Dermatology, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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