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Fixed Drug Eruption — RACP Adult Medicine MCQ

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EasyRheumatologyFixed Drug EruptionRACP Adult Medicine

A 45-year-old woman develops recurrent well-demarcated round erythematous-violaceous plaques in the same location on her inner thigh each time she takes doxycycline. The lesions leave post-inflammatory hyperpigmentation. What is the most likely drug rash?

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Correct answer: C — Fixed drug eruption

Recurrent well-demarcated plaques in the exact same anatomical location with each drug re-exposure leaving residual hyperpigmentation is fixed drug eruption. The lips, genitalia, and acral areas are most commonly affected. It is a type IV hypersensitivity reaction. The key diagnostic feature is recurrence at the identical site. Multiple drugs can cause it (NSAIDs, antibiotics, sulfonamides).

Reference: eTG Dermatology – 2024 – Fixed Drug Eruption