Half-moccasin distribution of acute tinea pedis

Clues to the diagnosis

Hyperkeratotic tinea pedis is commonly associated with interdigital tinea pedis; consequently, the lesions typically spread from the toes.³ In the acute phase, the lesions do not cover the entire plantar surface but extend from the toes to the middle of the sole, resulting in a “half-moccasin” distribution, as seen in this patient. Because the accuracy of a clinical diagnosis based solely on skin abnormalities such as erythema and hyperkeratosis is low,⁴ clinicians should also note the distribution of lesions. The half-moccasin distribution may be useful for diagnosing hyperkeratotic tinea pedis in the acute phase.

Differential diagnosis

The differential diagnosis of plantar erythema includes intertrigo, cellulitis, atopic dermatitis, contact dermatitis, eczema, juvenile plantar dermatosis, mycosis fungoides, and pityriasis rubra pilaris.¹ Potassium hydroxide testing, although useful for diagnosing hyperkeratotic tinea pedis and differentiating it from these diseases, is not always available, especially in primary care clinics.⁵ Therefore, clinical diagnosis based on a patient’s presentation is often necessary.

Treatment

The mainstay of treatment is topical antifungal therapy, generally applied once or twice daily for 1 to 6 weeks depending on severity and medication.¹ Response times vary by the type of tinea pedis: interdigital tinea pedis typically improves within 1 week, while hyperkeratotic tinea pedis usually requires 4 weeks due to keratinization impeding topical medication penetration.^1,2

Systemic antifungal treatment should be considered in patients with severe hyperkeratotic tinea pedis, extensive lesions, recurrent or chronic infection, or concomitant onychomycosis; in patients who are immunocompromised; or if topical treatment fails.^1,2 Topical treatments are generally effective, however, so inadequate treatment administration, antifungal resistance, and alternative diagnoses should be considered concurrently.