(See also Overview of Bacterial Skin Infections.)
Erythrasma resembles tinea or intertrigo. It most commonly affects the foot, where it manifests as superficial scaling, fissuring, and maceration typically confined to the 3rd and 4th web spaces. Erythrasma in the groin manifests as irregular but sharply marginated pink or brown patches with fine scaling. Erythrasma may also involve the axillae, submammary or abdominal folds, and perineum, particularly in obese middle-aged women and in patients with diabetes.
Erythrasma fluoresces a characteristic coral-red color under a Wood light due to production of porphyrin by the causative bacterium. Absence of hyphae in skin scrapings also distinguishes erythrasma from tinea.
Differential diagnosis of erythrasma includes perianal streptococcal cellulitis. Perianal streptococcal cellulitis causes pain and bright-red erythema solely on perianal skin and lacks fluorescence on Wood light examination. Cultures for group A streptococcus done on skin swabs from affected children are positive. Oral therapy that targets streptococcus is typically necessary to treat perianal streptococcal infection.
Treatment of erythrasma is a single dose of oral clarithromycin 1 g. Topical erythromycin, clindamycin, 2% mupirocin, fusidic acid, and benzoyl peroxide are also effective. Topical antiseptics containing chlorhexidine or benzalkonium chloride have been shown to be effective against Corynebacterium in vitro and might help patients with erythrasma.
One to two treatments (80 J/cm2) of broadband red light (635 nm) have been successful in a small case series. Recurrence is common.
If Wood light and potassium hydroxide (KOH) or fungal culture are not available to distinguish between erythrasma and superficial fungal infection, a combination of antibacterial and antifungal topical preparations should be considered.