Erythrasma

 

Introduction

Erythrasma is a common mild chronic localized superficial bacterial infection of the skin caused by a group of closely related aerobic coryneform bacteria, usually known as C. minutissimum. It is a common disease affecting the axillae, groins and toe webs which may be symptom free or show mild discomfort and itching.  It is commonly misdiagnosed as tinea cruris for many months before proper diagnosis is made.

 

Epidemiology

 

The organisms responsible are frequently members of the normal flora, at least in the toe clefts, and that some shift in the host–parasite relationship results in the development of classical erythrasma.

 

Age

Clinical infection may occur at any age but is more common among adults than children.

 

Sex

Erythrasma is more common in men.

 

Associated diseases

Erythrasma may be the presenting feature in diabetics

 

Environmental factors

A warm humid climate is a predisposing factor.

 

Clinical Features

The most common site of involvement is the web spaces of the feet, where erythrasma presents as a scaling, fissuring and white macerated plaque, especially between the fourth and fifth toes. In the genitocrural, axillary, and inframammary regions, the lesions present as well-demarcated, but irregular 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. In the groins, it affects the area of one or both thighs in contact with the scrotum. In the generalized form, the sharply marginated, reddish brown scaly lamellated plaques on the trunk, inguinal area, and web spaces of the feet.

Most lesions are asymptomatic, but may cause irritation of the lesions in the groins that may lead to secondary changes of excoriations and lichenification.

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 occurring predominantly on the upper trunk, and the individual lesions are small and are not erythematous.  Tinea cruris tends to have an active scaling border with central clearing. It is difficult to differentiate erythrasma of the toe clefts from tinea pedis or Candida infection, but, as in all varieties of erythrasma, the presence of coral‐red fluorescence under Wood's light is diagnostic. Since many patients have both tinea pedis and erythrasma, mycological examination of scales is important. 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. Scrapings from the affected skin may show rod-like, Gram-positive organisms in large numbers in Gram stain.

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% gel are effective in most cases. Erythrasma responds well to most topically applied azole antifungal agents, such as clotrimazole and miconazole. The duration of therapy varies, but 2 weeks is usually sufficient. Alternatives include topical fucidin and clindamycin solution. For widespread involvement, oral erythromycin is effective. A 1-g single dose of clarithromycin has been used successfully. Relapse is a problem in some patients. For secondary prophylaxis, an antibacterial benzoyl peroxide bar and drying agents, such as powders, in the affected areas should be used.