Tinea pedis with involvement of the fourth and fifth toe web spaces, presenting with maceration and erosion, is classified as which type?

Explanation

## Classification of Tinea Pedis by Morphology **Key Point:** Tinea pedis is classified into four morphological types based on clinical presentation and site of involvement. The interdigital type is the most common. ### Morphological Types of Tinea Pedis | Type | Site | Clinical Features | Causative Organism | Frequency | |------|------|------------------|-------------------|----------| | **Interdigital** | 4th & 5th toe web | Maceration, erosion, fissuring, scaling, pruritus | *T. rubrum*, *T. mentagrophytes* | Most common (60–70%) | | **Hyperkeratotic** | Sole, heel, lateral border | Dry scaling, hyperkeratosis, non-inflammatory | *T. rubrum* | 20–30% | | **Inflammatory/Bullous** | Sole, arch, lateral border | Vesicles, bullae, pustules, severe inflammation | *T. mentagrophytes*, *T. verrucosum* | 10–15% | | **Vesicular** | Sole, arch | Acute vesicles and bullae, intense pruritus | *T. mentagrophytes* | <5% | **High-Yield:** The **interdigital type** is the most common presentation of tinea pedis and typically affects the 4th and 5th toe web spaces due to: - Maximum moisture retention - Poor ventilation in this area - Maceration of the stratum corneum ### Clinical Characteristics of Interdigital Type **Clinical Pearl:** The interdigital type presents with: 1. **Maceration** — softening and whitening of the epidermis 2. **Erosion** — loss of the superficial epidermis 3. **Fissuring** — painful cracks in the skin 4. **Scaling** — fine, powdery desquamation 5. **Pruritus** — often intense and burning **Mnemonic:** **IMEF** = **I**nterdigital = **M**aceration, **E**rosion, **F**issuring (classic triad of the 4th–5th web space). ### Why the 4th–5th Web Space? The fourth and fifth toe web spaces are the most occluded and humid areas of the foot, creating an ideal microenvironment for dermatophyte proliferation and maceration of the epidermis.