A 28-year-old male manual labourer from Mumbai presents with a 3-week history of itching and scaling on the dorsal surfaces of both feet and between the toes. Examination reveals erythematous, scaly patches with a well-demarcated border and central clearing on the soles and lateral aspects of the feet. KOH mount from the scale shows septate hyphae. He reports that his gym locker-room mate had a similar condition last month. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Tinea Pedis ### Presentation Pattern The patient presents with the classic triad of tinea pedis: 1. **Location**: Dorsal feet, interdigital spaces, and soles — the most common site for dermatophyte infection 2. **Morphology**: Erythematous, scaly patches with well-demarcated borders and central clearing 3. **Epidemiology**: Occupational exposure (gym, shared facilities) and warm, humid climate (Mumbai) ### Mycological Confirmation **Key Point:** KOH mount showing septate hyphae confirms a dermatophyte infection. *Trichophyton rubrum* and *T. mentagrophytes* are the commonest causative agents in India. ### Site-Specific Characteristics of Tinea Pedis | Feature | Tinea Pedis | Tinea Corporis | Tinea Cruris | |---------|------------|----------------|---------------| | **Primary site** | Feet (interdigital, soles, dorsal) | Trunk, arms, legs | Groin, inner thighs, buttocks | | **Typical presentation** | Scaling, maceration, vesicles | Ring-shaped lesions on trunk | Bilateral, well-demarcated border | | **Risk factors** | Warm feet, occlusion, gym exposure | Direct contact, poor hygiene | Moisture, friction, obesity | | **Pruritus intensity** | Moderate to severe | Mild to moderate | Moderate to severe | ### Clinical Pearl **High-Yield:** Tinea pedis is the **most common dermatophytosis worldwide** and the **most frequent site of tinea in adults**. The interdigital (fourth toe web) variant is the most common presentation in India. ### Diagnostic Confirmation - **KOH mount**: Septate hyphae (as seen here) — diagnostic - **Culture**: Not routinely needed but *T. rubrum* or *T. mentagrophytes* would grow - **Wood's lamp**: Typically non-fluorescent (unlike *Microsporum* species) [cite:Inamadar & Palit, IJDVL 2003; Fitzpatrick's Dermatology 9e Ch 134]