Erythrasma Mimicking Tinea Versicolor: The Diagnostic Utility of Ultraviolet-Induced Fluorescence Dermoscopy and Successful Combination Therapy.

Erythrasma is a chronic superficial bacterial infection caused by Corynebacterium minutissimum, often misdiagnosed as dermatophytosis or pityriasis versicolor due to overlapping morphology. A 55-year-old gentleman presented to our Dermatology Department with itchy skin lesions that had progressed slowly over three years. On examination, scaly, hyperpigmented patches were noted, localized to the axillae and groins. He had taken multiple courses of antifungals without relief. Potassium hydroxide (KOH) examination showed no spores or hyphae; polarized dermoscopy demonstrated brown areas with scaling, and ultraviolet-induced fluorescence (UVF) dermoscopy showed coral-red fluorescence consistent with erythrasma. He received topical Whitolyn (salicylic acid 3% plus benzoic acid 6%) mixed with 2% fusidic acid twice daily, along with oral doxycycline 100 mg once daily for 20 days, and demonstrated significant clinical improvement, with complete disappearance of coral-red fluorescence on repeat UVF dermoscopy. UVF dermoscopy, by enhancing porphyrin fluorescence produced by C. minutissimum, serves as a rapid, non-invasive diagnostic and follow-up tool. It allows clear differentiation of erythrasma from mimickers such as tinea versicolor or candidiasis, which lack such fluorescence, thereby aiding in both accurate diagnosis and assessment of therapeutic efficacy.