Four weeks after an anaphylactic (Type I) reaction to a drug, a patient develops target / bull's-eye skin lesions around the mouth. What is the most likely diagnosis?

Correct answer: B. Erythema multiforme — treated with corticosteroids

• A. Stevens-Johnson syndrome is erythema multiforme major with systemic involvement — requires hospitalization, but the board answer for typical delayed target lesion management is corticosteroids.
• B. Correct. Target (bull's-eye) lesions appearing 2-4 weeks after a drug reaction (or following HSV reactivation) are ERYTHEMA MULTIFORME — a Type IV delayed hypersensitivity reaction. Treatment involves systemic corticosteroids to reduce the inflammatory response. Erythema multiforme minor has mucous membrane involvement and resolves; erythema multiforme major (Stevens-Johnson) is more severe.
• C. Urticaria (hives) are raised, itchy welts — not target lesions.
• D. Contact dermatitis presents as localized eczema-like reaction at the contact site — not target lesions.