Due to the condition’s persistence and the negative KOH prep, erythrasma was the most likely diagnosis.
Erythrasma is caused by a bacterial infection with Corynebacterium minutissimum. It occurs in intertriginous areas that tend to be moist and irritated by friction. The erythema is usually a dull red, rather than the bright red that one would see with yeast infections. In addition, there is typically central pallor.
Woods lamp examination can confirm the diagnosis by showing coral pink fluorescence. In this patient, however, there was no fluorescence because the patient had recently washed the area and, thus, removed the porphyrins produced by C minutissimum. Biopsy for pathology is not usually necessary.
Erythrasma is treated with topical clindamycin, fusidic acid, or mupirocin. Oral macrolides and tetracyclines are also effective.1 Due to the chronicity of the erythrasma and the discomfort it caused, this patient opted for oral doxycycline 100 mg twice daily for 10 days. At follow-up 2 weeks later, the erythrasma had resolved.
Photo and text courtesy of Daniel Stulberg, MD, FAAFP, Department of Family and Community Medicine, University of New Mexico School of Medicine, Albuquerque