A 28-year-old male farmer from rural Maharashtra presents with a 6-week history of itching and scaling on his feet. On examination, he has erythematous, scaly patches involving the soles, lateral borders, and interdigital spaces of both feet. The lesions are well-demarcated with a raised edge. KOH mount from the scale shows branching septate hyphae. He reports the condition worsened during the monsoon season. What is the most likely diagnosis?

Explanation

## Diagnosis: Tinea Pedis (Interdigital Type) ### Clinical Presentation **Key Point:** Tinea pedis is the most common dermatophyte infection worldwide, accounting for ~70% of all dermatophyte infections. The interdigital variant is the most frequent presentation. ### Site-Specific Features of Tinea Pedis | Feature | Interdigital Type | Plantar (Moccasin) Type | Vesicular Type | |---------|-------------------|------------------------|----------------| | **Location** | 4th–5th toe web space (classic) | Sole, heel, lateral border | Plantar arch, sole | | **Appearance** | Maceration, scaling, erythema | Diffuse scaling, hyperkeratosis | Vesicles, pustules, erosions | | **Pruritus** | Mild to moderate | Mild | Severe, acute onset | | **Seasonality** | Worse in monsoon/humidity | Chronic, persistent | Acute flares | | **KOH Mount** | Branching septate hyphae | Branching septate hyphae | Branching septate hyphae | **High-Yield:** The **interdigital space between the 4th and 5th toes** is the classic site for tinea pedis — this is where moisture and occlusion are maximal. ### Why This Case Fits Tinea Pedis 1. **Farmer in monsoon region** — high humidity and occlusion from footwear 2. **Interdigital and sole involvement** — typical distribution pattern 3. **Well-demarcated, raised edge** — characteristic of dermatophyte infection 4. **KOH positive for branching septate hyphae** — confirms dermatophyte (not Candida, which is pseudohyphae) 5. **Seasonal worsening** — moisture and heat exacerbate tinea pedis ### Causative Organisms **Mnemonic: TEC** — *Trichophyton mentagrophytes, Epidermophyton floccosum, Candida (NOT a dermatophyte)* - *Trichophyton rubrum* (most common, ~60–70%) - *Trichophyton mentagrophytes* (second most common) - *Epidermophyton floccosum* **Clinical Pearl:** Tinea pedis is rare before age 10 and increases with age; it is more common in males and in warm, humid climates. ### Management Approach - **Topical azoles** (miconazole, clotrimazole) for localized interdigital disease - **Systemic antifungals** (terbinafine 250 mg daily × 2–4 weeks, or itraconazole) for extensive or plantar involvement - **Hygiene measures:** keep feet dry, avoid occlusive footwear, use antifungal powder [cite:Fitzpatrick's Dermatology 9e Ch 130]