A 32-year-old woman develops a sharply demarcated dusky erythematous plaque at the same site on her ankle after each course of cotrimoxazole. Biopsy of the lesion shows basal layer necrosis, an interface infiltrate of lymphocytes with eosinophils scattered through all levels of the dermis, pigment incontinence and thrombosed dilated capillaries. What is the diagnosis?

• A Sweet syndrome
• B Erythema multiforme major
• C Lichen planus
• D Fixed drug eruption ✓

Explanation

Fixed drug eruption recurs at identical sites after rechallenge with the offending drug. Its biopsy shows interface dermatitis with basal cell necrosis, eosinophils distributed throughout the dermis, deep perivascular inflammation, melanophages from previous attacks, and often dermal capillary thrombi. Erythema multiforme lacks recurrent site specificity and shows a tighter lymphocytic interface reaction without pan-dermal eosinophils, while Sweet syndrome is a neutrophilic dermatosis without interface change.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.