Photo Rounds

“Jock itch” or something else?

A 32-year-old man presented to his family physician with a rash in his groin that he’d had for over 6 months. He was athletic and assumed that the rash was “jock itch.” He had tried an over-the-counter topical antifungal medicine, but it hadn’t provided any relief. The patient was in otherwise good health.

What’s your diagnosis?


The family physician (FP) agreed that this could be a tinea cruris infection. He performed a potassium hydroxide (KOH) preparation, but did not see any hyphae or fungal elements. (See video on how to perform a KOH preparation here.)

He told the patient that there was no evidence of fungus under the microscope, and took out his Woods lamp (ultraviolet light) to check for erythrasma. The involved area fluoresced a coral red, confirming the diagnosis of erythrasma. Erythrasma is a bacterial infection caused by Corynebacterium minutissimum.

Treatment options include topical erythromycin, topical clindamycin, oral erythromycin, or oral clarithromycin. The patient decided to take oral erythromycin and the FP prescribed 250 mg twice a day for 2 weeks. At a follow-up visit one month later, the rash had completely resolved.

Photos and text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Usatine R, Smith M. Tinea cruris. In: Usatine R, Smith M, Mayeaux EJ, et al, eds. Color Atlas of Family Medicine. 2nd ed. New York, NY: McGraw-Hill; 2013:795-798.

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