A 28-year-old male farmer from rural Maharashtra presents with a 6-week history of progressive itching and scaling on his feet. On examination, he has erythematous, scaly patches with a characteristic 'moccasin' distribution involving the sole, lateral border, and heel of both feet. The toenails appear normal. KOH mount from scale shows septate hyphae. He has tried multiple topical antifungals without improvement. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Tinea Pedis — Moccasin Type **Key Point:** The moccasin type of tinea pedis is characterized by a **chronic, non-inflammatory distribution** involving the sole, lateral border, and heel — mimicking a moccasin shoe. ### Distinguishing Features of Tinea Pedis Variants | Feature | Interdigital | Moccasin | Vesiculobullous | Ulcerative | |---------|--------------|----------|-----------------|------------| | **Location** | Web spaces (4th–5th toe) | Sole, heel, lateral border | Instep, arch | Sole, heel | | **Appearance** | Maceration, fissuring | Dry scaling, erythema | Vesicles, bullae | Erosions, ulcers | | **Onset** | Acute, pruritic | Chronic, insidious | Acute, painful | Chronic, severe | | **Common Organism** | *T. mentagrophytes* | *T. rubrum* | *T. mentagrophytes* | *T. rubrum* | | **Response to Rx** | Good | Poor (chronic) | Excellent | Variable | **High-Yield:** Moccasin-type tinea pedis is the **most common presentation** in tropical countries like India and is caused predominantly by *Trichophyton rubrum*. It is **chronic and often refractory** to topical therapy, requiring systemic antifungals. ### Clinical Pearl **Clinical Pearl:** The moccasin type often presents as **dry, scaly dermatitis** rather than the acute, inflammatory interdigital form. Patients may mistake it for eczema or psoriasis. The **normal nails** rule out onychomycosis as the primary pathology. ### Why Systemic Therapy Is Needed 1. Chronic nature with poor topical penetration to thick sole skin 2. High recurrence rate (up to 50%) with topical agents alone 3. Often associated with nail involvement (subclinical) **Mnemonic:** **MOCCASIN = Moist (chronic), Chronic, Sole-centered, Insidious, Systemic therapy needed** [cite:Valia & Valia Dermatology 3e] ## Management Algorithm ```mermaid flowchart TD A[Moccasin-type Tinea Pedis Confirmed]:::outcome --> B{Nail involvement?}:::decision B -->|No| C[Systemic azole: Terbinafine 250 mg daily × 4 weeks]:::action B -->|Yes| D[Terbinafine 250 mg daily × 6–12 weeks]:::action C --> E[Add topical agent for symptomatic relief]:::action D --> E E --> F[Review at 4 weeks, repeat KOH if needed]:::action F --> G[Counsel on prevention: dry feet, antifungal powder]:::action ```