Erythrasma is a localized, mild and sometimes chronic skin infection mainly localized to the skin folds. It’s very common, affecting males more than females, with a prevalence approaching 20%. The interdigital variant may be the most common bacterial skin infection. Adults are affected more often than children.

Pathogenesis

Erythrasma is a mild bacterial skin infection caused by Corynebacterium minutissimum, a gram-positive rod. It’s often part of the normal skin flora. In erythrasma, we find excessive proliferation of C. minutissimum within the stratum corneum, especially in moist, occluded areas.

Clinical features

Erythrasma is predominantly an eruption of the flexural surfaces, such as the web spaces, axillae, inframammary folds, groin and intergluteal fold. It’s rarely found outside of the folds, and this variant is known as “disciform.” Disciform erythrasma is associated with diabetes mellitus.

Lesions are well-demarcated pink to red plaques that fade to brown over time. Sometimes there are fine scales, with a wrinkled appearance. Unlike tinea, though, there’s no central clearing. Hyperpigmentation is common, especially in darker skin types. Occasionally, lesions can be macerated.

The interdigital variant is characterized by white maceration with fissuring and yellow hyperkeratosis in the web spaces; the 4^th web space is the most common.

Erythrasma is mainly asymptomatic. Occasionally, lesions are itchy, especially when the groin is involved. Scratching can lead to increased skin markings and thickening- lichenification.

Investigations

Erythrasma is often a clinical diagnosis but tests, both in-office and microbiological, are confirmatory.

A Wood’s lamp is a source of UV light with a 365 nm peak wavelength. When exposed, lesions of erythrasma will fluoresce bright “coral red,” due to the production of coproporphyrin III by C. minutissimum. Pigment is within a thick stratum corneum, so it may persist even after the organism is cleared.

A skin swab can be sent for bacterial culture and sensitivity. Fungal microscopy and culture can be done on skin scrapings. Co-infections are common with dermatophytes or yeasts, especially in the web spaces.

Skin biopsy is seldom helpful, as features are non-specific. Sometimes a gram stain on the biopsy specimen will show organisms in the stratum corneum.

Treatment

Erythrasma typically has a benign course and lesions are mostly asymptomatic. Lesions can have exacerbations or recur after successful treatment.

Treatment is often sought for improvement of associated itch, or cosmesis. Fissuring is a risk factor for cellulitis.

To prevent further infections and for initial treatment, advise patients to use antibacterial soap washes. Such washes should be done daily while treating infection, and 2-3 times weekly to prevent recurrences. Benzoyl peroxide-containing soaps are often effective.

Topical therapies are the mainstay. These include antifungals that also have activity against gram-positive bacteria, e.g. azoles and topical antibiotics. Clotrimazole cream is a good option if there is concern about co-existing fungal or yeast infection as it’s also effective against C. minutissimum. When used twice daily over 2-4 weeks, it will clear erythrasma in the majority of patients.

Topical antibacterials such as benzoyl peroxide 5% gel, fusidic acid creams and clindamycin 1-2% preparations are also effective when used twice daily for about 2 weeks.

For cases that don’t respond to topical therapies or for widespread cases, either reconsider the diagnosis — see Table 2 and investigations above — or consider oral antibiotics, preferably with anti-inflammatory properties. Erythromycin can be dosed at 250 mg po 4 times daily for 5-7 days. Another option is a single dose of clarithromycin 1 g po. Combinations are sometimes used for resistant infections.