A 28-year-old woman presents with a scaly, erythematous patch on her scalp with hair loss. Microscopy shows endothrix spores. In contrast, a colleague describes a patient with tinea corporis presenting with an expanding annular lesion with central clearing on the trunk. Which feature best distinguishes tinea capitis from tinea corporis?

Explanation

## Distinguishing Tinea Capitis from Tinea Corporis ### Structural and Anatomical Differences | Feature | Tinea Capitis | Tinea Corporis | |---------|---------------|----------------| | **Site of infection** | Hair shaft, hair follicle, scalp epidermis | Glabrous (non-hairy) skin: trunk, limbs, face | | **Hair involvement** | Direct invasion of hair shaft (endothrix/ectothrix) | No hair follicle invasion; hairs may be shed but not infected | | **Alopecia type** | Non-scarring (usually) or scarring (if severe/chronic) | No alopecia; hairs are not destroyed | | **Permanence of damage** | Potential for permanent scarring alopecia (e.g., favus) | No permanent structural damage | | **Clinical morphology** | Scaly patches, pustules, kerion, favus | Annular lesions with central clearing (ringworm) | | **Causative organisms** | Microsporum canis, M. audouinii, T. tonsurans, T. violaceum | T. rubrum, T. mentagrophytes, E. floccosum | **Key Point:** The **fundamental distinction** is that tinea capitis involves the **hair shaft and follicle** (with risk of permanent scarring alopecia), whereas tinea corporis is confined to **glabrous skin without hair follicle invasion**. ### Pathophysiology of Site-Specific Infection 1. **Tinea capitis**: Dermatophytes invade the hair cortex and medulla - Endothrix: spores within hair shaft (T. tonsurans, T. violaceum) - Ectothrix: spores on hair surface (M. canis, M. audouinii) - Risk of folliculitis and permanent scarring 2. **Tinea corporis**: Infection limited to stratum corneum of glabrous skin - No invasion of hair follicles - Hairs may be shed but are not infected - No permanent scarring **Clinical Pearl:** A kerion (severe pustular reaction) in tinea capitis indicates host immune response to follicular invasion and is a sign of potential permanent scarring. This does not occur in tinea corporis. **High-Yield:** The **presence of hair follicle invasion in tinea capitis versus absence in tinea corporis** is the single most important discriminator. This explains why tinea capitis carries risk of permanent alopecia while tinea corporis does not. **Mnemonic:** **SCALP** (Shaft, Cortex, Alopecia, Loss, Permanent) for tinea **Capitis** vs. **SKIN** (Surface, Keratinous layer, Intact follicles, No alopecia) for tinea **Corporis**. [cite:Fitzpatrick's Dermatology in General Medicine Ch 132]