Inguinal Erythrasma
A 38-year-old man presented to the dermatology clinic with a 9-month history of a mildly itchy rash in his groin. The rash had been previously diagnosed as tinea cruris, but it had not abated with topical antifungal treatment. On physical examination, the patient’s vital signs were normal. Well-circumscribed, reddish-brown plaques were observed in the inguinal folds when the patient elevated his genitals (Panel A). No scaling or satellite lesions were present. A potassium hydroxide preparation of skin scrapings from the lesions was negative for fungal organisms. Under a Wood’s lamp, the rash showed coral-red fluorescence (Panel B). Corynebacterium minutissimum grew on a bacterial culture of skin scrapings. A diagnosis of inguinal erythrasma was made. Erythrasma is a superficial bacterial skin infection caused by C. minutissimum. It typically manifests in the intertriginous or interdigital areas. Erythrasma may be mistaken for a superficial fungal skin infection, but it can be differentiated from a dermatophytosis by its reddish-brown color and minimal scaling. A Wood’s lamp examination facilitates diagnosis owing to the characteristic coral-red fluorescence, which is caused by porphyrins produced by the bacteria. After a course of topical mupirocin and oral erythromycin, the rash had abated at the 2-week follow-up.