Tinea pedis presenting with maceration, erosion, and fissuring primarily between the fourth and fifth toes is most commonly caused by which organism?

Explanation

## Tinea Pedis: Interdigital (Toe Web) Variant **Key Point:** The interdigital form of tinea pedis—characterized by maceration, erosion, and fissuring between the toes (especially the 4th–5th web space)—is most commonly caused by *Trichophyton mentagrophytes*. ### Site-Specific Presentation of Tinea Pedis | Variant | Location | Features | Common Organism | |---------|----------|----------|------------------| | Interdigital | 4th–5th toe web (most common) | Maceration, erosion, fissuring, pruritus | **T. mentagrophytes** | | Plantar (moccasin type) | Sole and lateral foot | Hyperkeratosis, scaling, minimal inflammation | T. rubrum | | Vesiculobullous | Arch and lateral sole | Vesicles, pustules, severe pruritus | T. mentagrophytes | | Onychomycosis | Toenails | Nail thickening, discoloration, crumbling | T. rubrum, T. mentagrophytes | **High-Yield:** *Trichophyton mentagrophytes* is the **classic organism for interdigital tinea pedis**. It is strongly associated with the acute, inflammatory, macerated, and fissured presentation in the toe webs, particularly the 4th–5th interdigital space. **Clinical Pearl:** While *T. rubrum* is the most common dermatophyte overall (causing moccasin-type tinea pedis and onychomycosis), *T. mentagrophytes* is classically implicated in the interdigital (web space) variant with maceration and fissuring. *Epidermophyton floccosum* can also cause interdigital tinea pedis but is not the most common cause. ### Why T. mentagrophytes Causes Interdigital Disease? 1. Produces potent keratinases and proteinases that cause acute inflammatory reactions 2. Thrives in warm, moist, occluded environments such as toe webs 3. Anthropophilic strains are well-adapted to human stratum corneum 4. Associated with acute inflammatory tinea pedis presentations **Reference:** Andrews' Diseases of the Skin (12th ed.) and Fitzpatrick's Dermatology (9th ed.) both list *T. mentagrophytes* as the primary causative organism of interdigital tinea pedis with maceration and fissuring. **Mnemonic:** **T. Mentagrophytes** = **M**acerated, **M**oist, interdigital toe web disease.