ERYTHRASMA
Erythrasma is a common superficial bacterial infection of the skin characterized by well-defined but irregular reddish brown patches, occurring in the intertriginous areas, or by fissuring and white maceration in the toe clefts.
Etiology and Epidemiology.
C. minutissimum, the etiologic agent of erythrasma, is a short, Gram-positive rod with subterminal granules. The infection is more common in tropical than in temperate climates. In a study in a temperate climate, 20 percent of randomly selected subjects were found to have erythrasma by Wood's lamp examination. The generalized disease is much more common in the tropics. Erythrasma is more common in men and may occur in asymptomatic form in the genitocrural area.
Clinical Findings.
HISTORY.
Symptoms vary from a completely asymptomatic form, through a genitocrural form with considerable pruritus, to a generalized form with scaly lamellated plaques on the trunk, inguinal area, and web spaces of the feet. When pruritic, irritation of lesions may cause secondary changes of excoriations and lichenification.
CUTANEOUS LESIONS.
The most common site of involvement is the web spaces of the feet, where erythrasma presents as a hyperkeratotic white macerated plaque , especially between the fourth and fifth toes. In the genitocrural, axillary, and inframammary regions, the lesions present as well-demarcated, reddish-brown, superficial, finely scaly, and finely wrinkled patches . In these sites, the patches have a relatively uniform appearance as compared with tinea corporis or cruris, which often have central clearing.
Wood's lamp examination of erythrasma reveals a coral-red fluorescence caused by coproporphyrin III. The fluorescence may persist after eradication of the Corynebacterium as the pigment is within a thick stratum corneum.
DIFFERENTIAL DIAGNOSIS.
Tinea versicolor is distinguished from erythrasma by the lesions on the trunk being most numerous at nonintertriginous sites. Tinea cruris tends to have an active scaling border with central clearing. Inverse psoriasis usually presents as sharply demarcated plaques with a shiny red color in the intergluteal cleft, inguinal folds, and axillae.
LABORATORY FINDINGS.
Culture of the specific Corynebacterium in abundance from the lesion corroborates the diagnosis. Gram-stained imprints of the horny layer of the skin show rod-like, Gram-positive organisms in large numbers.
The diagnosis is strongly suggested by the location and superficial character of the process, but must be confirmed by demonstration of the characteristic “coral-red” fluorescence with Wood's lamp illumination.
PROGNOSIS AND CLINICAL COURSE.
The disease may remain asymptomatic for years or may undergo periodic exacerbations. Relapses occasionally occur even after successful antibiotic treatment.
TREATMENT.
For localized erythrasma, especially of the web spaces of the feet, benzoyl peroxide wash and 5 percent gel are effective in most cases. Clindamycin (2 percent solution) or azole creams are several of the many effective topical agents. For widespread involvement, oral erythromycin is effective. A 1 g single dose of clarithromycin has been used successfully. For secondary prophylaxis, an antibacterial benzoyl peroxide bar when showering is effective.