tinea pedis
Summary
Tinea pedis (athlete's foot) is a dermatophyte infection of the feet, most commonly caused by Trichophyton rubrum. It presents with interdigital scaling, maceration, pruritus, and can involve the soles in a 'moccasin' distribution.
Detail
Tinea pedis is a superficial fungal infection caused by dermatophytes (Trichophyton rubrum, T. mentagrophytes, Epidermophyton floccosum) that invade the stratum corneum using keratinase enzymes. It is the most common dermatophyte infection worldwide, favored by warm, moist environments (communal showers, occlusive footwear, sweating). Clinical patterns include: interdigital type (most common, maceration/scaling between toes, often 4th-5th web space), moccasin type (chronic hyperkeratotic scaling of soles and lateral foot), and vesiculobullous type (acute, painful vesicles/bullae, often on the instep). Diagnosis is clinical but confirmed via KOH prep showing septate branching hyphae, or fungal culture on Sabouraud agar. Wood's lamp is NOT useful for dermatophytes (unlike tinea versicolor caused by Malassezia). Tinea pedis can serve as a portal of entry for bacterial cellulitis (especially in diabetics or immunocompromised patients) and can spread to nails (onychomycosis) or groin (tinea cruris) via autoinoculation - remember 'one hand, two feet' distribution pattern for chronic dermatophytosis. Treatment includes topical antifungals (terbinafine, clotrimazole, azoles) for localized disease; oral antifungals (terbinafine, itraconazole) for extensive, moccasin-type, or refractory cases. Prevention includes keeping feet dry, wearing breathable footwear, and avoiding barefoot contact in communal areas.
Sources
- First Aid for the USMLE Step 1
- Fitzpatrick's Dermatology
- UpToDate: Dermatophyte infections
- Sabiston Textbook of Surgery (for complications)
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