A 35-year-old female schoolteacher from Delhi presents with a 6-week history of progressive hair loss and scaling on the scalp. Examination shows circular patches of alopecia with broken hairs at the margin, erythema, and fine scale. She reports mild pruritus. Wood's lamp examination shows a faint blue-green fluorescence. Pluck hair shows spores arranged in a sheath-like pattern around the hair shaft (endothrix pattern). What is the most likely causative organism?

Explanation

## Diagnosis: Tinea Capitis Caused by *Trichophyton tonsurans* ### Clinical Presentation of Tinea Capitis **Key Point:** Tinea capitis is a dermatophyte infection of the scalp hair and follicles, presenting with alopecia, scaling, and pruritus. The causative organism varies by geography and epidemiology. ### Diagnostic Features in This Case | Feature | Finding | Significance | |---------|---------|-------------| | **Site** | Scalp with circular alopecia | Classic for tinea capitis | | **Morphology** | Broken hairs at margin, erythema, scale | Inflammatory tinea capitis pattern | | **Microscopy** | Endothrix pattern (spores in sheath around hair) | Indicates *Trichophyton* species | | **Wood's lamp** | Faint blue-green fluorescence | Suggests *Microsporum* involvement, but NOT diagnostic | | **Geography** | Delhi, urban India | *T. tonsurans* increasingly common in India | ### Endothrix vs. Ectothrix Patterns **Mnemonic: ENDO-IN** — Endothrix spores are INSIDE the hair shaft; **ECTO-OUT** — Ectothrix spores are OUTSIDE the hair shaft. | Pattern | Location | Organisms | Fluorescence | |---------|----------|-----------|---------------| | **Endothrix** | Inside hair shaft | *T. tonsurans*, *T. violaceum*, *T. mentagrophytes* | Usually non-fluorescent | | **Ectothrix** | Outside hair shaft | *M. canis*, *M. audouinii*, *T. mentagrophytes* | Often fluorescent (blue-green) | ### Why *Trichophyton tonsurans*? **High-Yield:** *T. tonsurans* is now the **most common cause of tinea capitis in India and many urban areas worldwide**. It is an endothrix organism and typically does NOT fluoresce under Wood's lamp (though faint fluorescence can occur in some strains). The endothrix pattern (spores within the hair shaft) is the key identifying feature. **Clinical Pearl:** The faint blue-green fluorescence in this case is atypical for *T. tonsurans* but can occur; however, the **endothrix pattern on microscopy is pathognomonic** and overrides the Wood's lamp finding. *T. tonsurans* causes a more inflammatory presentation with broken hairs and erythema, consistent with this case. ### Epidemiology in India ```mermaid flowchart TD A["Tinea Capitis in India"]:::outcome --> B{"Organism?"}:::decision B -->|"Endothrix pattern"| C["*T. tonsurans* (most common, urban)"]:::action B -->|"Ectothrix pattern"| D["*M. canis* or *M. audouinii*"]:::action C --> E["Inflammatory, broken hairs"]:::outcome D --> F["Often fluorescent on Wood's lamp"]:::outcome E --> G["Systemic antifungal required"]:::action F --> G ``` ### Management **Key Point:** Tinea capitis requires **systemic antifungal therapy** because topical agents do not penetrate the hair shaft adequately. - **First-line:** Griseofulvin 20 mg/kg/day for 6–8 weeks (microsize) or terbinafine 125–250 mg daily for 4 weeks - **Adjunct:** Antifungal shampoo (ketoconazole 2% or selenium sulfide) 2–3 times weekly to reduce spore shedding - **Cure assessment:** Repeat KOH mount or culture at 4 weeks post-treatment