Erythrasma — SCE Dermatology MCQ

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EasyCutaneous InfectionErythrasmaSCE Dermatology

A 30-year-old woman presents with a well-defined erythematous plaque in the left axilla that does not respond to topical antifungals. She has a similar lesion on the right axilla. Wood lamp examination shows coral-red fluorescence. What is the diagnosis?

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Correct answer: E — Erythrasma

Erythrasma is a superficial bacterial infection caused by Corynebacterium minutissimum affecting intertriginous areas (axillae, groin, toe webs). The pathognomonic coral-red (pink-red) fluorescence under Wood lamp is due to bacterial production of porphyrins (coproporphyrin III). It presents as well-defined brown-red patches/plaques without significant scaling. Treatment is topical Fusidic acid or Clindamycin, or oral Erythromycin for extensive disease. Tinea does not fluoresce coral-red (Microsporum shows green fluorescence). Candidal intertrigo shows satellite pustules.

Reference: BAD 2016 Skin Infection Guidelines; DermNet NZ