Diagnosis: Erythrasma
The Wood’s lamp revealed a coral-red fluorescence in the interdigital spaces (FIGURE 2), which led us to a diagnosis of erythrasma.
The coral-red fluorescence seen under the Wood’s lamp is due to porphyrins produced by Corynebacterium minutissimum. The organism invades the stratum corneum where it proliferates and causes erythrasma. Erythrasma typically appears as delineated, dry, red-brown patches in intertriginous areas, such as the axilla, groin, interdigital spaces, intergluteal cleft, perianal skin, and inframammary area.1,2
Interdigital erythrasma is more common than previously thought; in one study of 151 patients with erythrasma, the most common site was the toe webs (64.9%), followed by the inguinal region (17.9%), the axillary region (14.6%), and the inframammary region (2.6%).2 Erythrasma affects 4% of the population; risk factors include poor hygiene, hyperhidrosis, obesity, warm climate, diabetes, and an immunocompromised state.3
Differential includes “athlete’s foot”
The differential diagnosis for a pruritic rash between the toes includes:
Tinea pedis. Erythrasma is often mistaken for tinea pedis, because both conditions cause scaling between the toes. A Wood’s lamp exam can quickly differentiate between the 2,1 as tinea pedis does not fluoresce under ultraviolet light.
Contact dermatitis mimics many conditions, but a negative Wood’s lamp exam and history of worsening with contact to specific substances helps to make this diagnosis.
Prevention and Tx hinge on good hygiene, topical agents
First-line management of erythrasma includes both nonpharmacologic and pharmacologic modalities. Good hygiene and, depending on the area affected, loose-fitting cotton undergarments can help treat and prevent erythrasma.
Topical 2% miconazole bid for 2 weeks has resulted in clearance rates as high as 88%.4 Its affordable price, over-the-counter availability, and lack of adverse effects make miconazole a reasonable choice.4,5 It is also a smart treatment choice when erythrasma is coexisting with tinea, because it can treat both conditions. This is not uncommon in the interdigital spaces between the toes and in the groin.
Topical 1% clindamycin or 2% erythromycin solution or gel bid for 2 weeks can also be used to treat the condition.3,6 However, given that topical antibiotics are more expensive than single-dose oral treatment and are no better than the oral formulations of these antibiotics,6 clarithromycin 1 g taken once orally may be preferred.2,6
Our patient was treated with a single dose of clarithromycin 1 g. At follow-up, her erythrasma was clear.
CORRESPONDENCE
Richard P. Usatine, MD, University of Texas Health at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX 78229; Usatine@uthscsa.edu.