A 41-year-old man presented with a pruritic rash between his toes that had been present for at least 2 months. Treatment with a nonprescription antifungal cream had not led to significant improvement. He did not have any other skin problems, and a review of systems was unremarkable.

Physical examination revealed moist, macerated, pinkish plaques in the fourth interdigital web spaces bilaterally (Figure 1). Wood lamp examination revealed a distinct coral-red fluorescence.

QUESTION

Based on the patient’s history and physical examination, which one of the following is the most likely diagnosis?

• A. Dyshidrotic eczema.

• B. Erythrasma.

• C. Mixed toe web infection.

• D. Psoriasis.

• E. Tinea pedis.

DISCUSSION

The answer is B: erythrasma. This superficial bacterial infection of the skin typically occurs in moist areas such as the interdigital web spaces, groin, axillae, and inframammary fold.¹ It is caused by the growth of Corynebacterium minutissimum, gram-positive rods that are part of the natural skin microbiome. Growth is accelerated by heat, moisture, and patient factors, including older age, diabetes, obesity, immunosuppression, hyperhidrosis, and poor hygiene.^1,2 Erythrasma comprises up to 17.6% of bacterial skin infections in older patients. The interdigital variety is encountered often in the clinical setting and is the most common bacterial foot infection. C minutissimum cellulitis and bacteremia are rare and occur primarily in immunocompromised individuals.^1,2