Erythrasma

For several months, a 49-year-old man had a light tan lesion with a sharp, irregular border in the groin. The lesion was asymptomatic. It tended to recur in hot weather, particularly when he had been sweating heavily. Wood light examination of the lesion revealed coral-red fluorescence.

Erythrasma is a superficial skin infection caused by Corynebacterium minutissimum, which is part of the normal skin flora. It can easily be confused with tinea cruris. However, in contrast, erythrasma is non-inflammatory, is lighter brown in color, has no advancing border, and exhibits coral-red fluorescence under a Wood light.

Risk factors for erythrasma include diabetes mellitus, warm climate, and occluded skin. It generally affects adults and is usually asymptomatic, but it may burn or itch. Erythrasma is most common in the intertriginous areas, including the groin, inframammary region, and axillae; the fourth toe interspace is the most common site.¹

In most patients, the diagnosis is made on the basis of the history and the gross appearance of the lesion. The differential diagnosis includes dermatophytosis, candidiasis, and seborrheic dermatitis. Coral-red fluorescence under a Wood light and the absence of hyphae on a potassium hydroxide smear help exclude fungal and yeast infections. Gram staining shows gram-positive rods in long filaments, but scale slide fixation is difficult, with resulting low yield, and is little used. Skin biopsy also shows rods and filaments superficially in the keratotic layer, but this test is rarely necessary.

Treatment options include oral erythromycin or clarithromycin; topical miconazole, clotrimazole, or econazole; topical clindamycin or erythromycin; and benzoyl peroxide.¹ This patient was treated with miconazole cream, and the rash resolved. 

REFERENCE:

1.Habif TP. Clinical Dermatology: A Color Guide to Diagnosis and Therapy. 4th ed. Philadelphia, PA: Mosby; 2004:419.