Tinea pedis caused by Trichophyton rubrum typically presents with which clinical pattern?

Explanation

## Clinical Presentation of Tinea Pedis by Organism **Key Point:** The clinical morphology of tinea pedis varies with the causative organism. T. rubrum causes a chronic, indolent infection characterized by interdigital involvement with minimal inflammation. **High-Yield:** T. rubrum tinea pedis is the most common type worldwide and typically presents as a **chronic interdigital dermatophytosis** with maceration, scaling, and fissuring, often affecting the fourth and fifth toe webs first. ## Three Main Clinical Patterns of Tinea Pedis | Pattern | Organism | Presentation | Inflammation | Duration | |---------|----------|--------------|--------------|----------| | **Interdigital (most common)** | T. rubrum, T. mentagrophytes var. mentagrophytes | Maceration, scaling, fissuring in toe webs (4th–5th web first) | Minimal to mild | Chronic, indolent | | **Plantar/Moccasin type** | T. rubrum | Diffuse scaling on sole and lateral foot; "moccasin" distribution | Minimal | Chronic, very resistant to treatment | | **Vesiculobullous/Acute** | T. mentagrophytes var. mentagrophytes | Vesicles and bullae, often on arch or lateral sole | Marked | Acute, often secondary bacterial infection | **Clinical Pearl:** T. rubrum causes a **dry, scaly** interdigital infection, whereas T. mentagrophytes causes an **acute, inflammatory** vesiculobullous pattern. The difference reflects their anthropophilic vs. zoophilic adaptation. **Mnemonic — "TRIM" for T. rubrum Tinea Pedis:** - **T** — Toe webs (interdigital) - **R** — Rubrum (T. rubrum) - **I** — Indolent (chronic, minimal inflammation) - **M** — Maceration and scaling ## Why Interdigital Involvement? 1. Toe webs provide warm, moist, occluded environment 2. Fourth and fifth toe webs are most occluded 3. T. rubrum thrives in chronic, low-inflammation conditions 4. Minimal immune response allows slow, persistent growth