A 28-year-old male labourer from rural Maharashtra presents with a 3-week history of intense pruritus and painful erosions on the groin, inner thighs, and scrotum. Examination reveals well-demarcated erythematous plaques with a raised, active border and central clearing. KOH mount from the lesion shows septate hyphae. The patient reports the rash worsened after sweating during monsoon season. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Tinea Cruris ### Key Clinical Features **Key Point:** Tinea cruris ("jock itch") is a dermatophyte infection of the groin, inner thighs, and scrotum, classically presenting in warm, humid climates and in individuals with poor hygiene or excessive sweating. ### Diagnostic Criteria Met in This Case | Feature | Finding in Case | Significance | |---------|-----------------|-------------| | **Site** | Groin, inner thighs, scrotum | Classic for tinea cruris | | **Border** | Well-demarcated, raised, active edge with central clearing | Pathognomonic for dermatophyte infection | | **Mycology** | Septate hyphae on KOH mount | Confirms fungal infection (dermatophyte) | | **Trigger** | Monsoon/sweating season | Warm, humid environment favours *Trichophyton* spp. | | **Symptom** | Intense pruritus with erosions | Typical inflammatory response | ### Causative Organisms **Mnemonic: TER** — *Trichophyton rubrum*, *Epidermophyton floccosum*, *T. mentagrophytes* - *Trichophyton rubrum* is the most common cause globally (70–80% of cases) - *T. mentagrophytes* is common in India and tropical regions - *Epidermophyton floccosum* is less common but still significant ### Distinguishing Features from Differentials **High-Yield:** Tinea cruris does NOT typically involve the scrotum itself (unlike candidiasis), but can extend to the inner thighs and inguinal folds. The **active raised border with central clearing** is the hallmark. ### Clinical Pearl **Clinical Pearl:** In tinea cruris, the scrotum may appear involved but the true dermatophyte infection spares the scrotum proper — the inflammation is in the adjacent skin. This is a key distinguishing point from candidiasis, which readily colonizes the scrotum. ### Management Approach ```mermaid flowchart TD A["Tinea Cruris Confirmed<br/>KOH positive, raised border"]:::outcome --> B{"Extent & Severity?"}:::decision B -->|"Localized, mild-moderate"| C["Topical azole<br/>Miconazole/Clotrimazole 2-3 weeks"]:::action B -->|"Extensive or refractory"| D["Systemic antifungal<br/>Terbinafine 250 mg daily x 2-4 weeks"]:::action C --> E["Hygiene counselling<br/>Keep area dry, cotton underwear"]:::action D --> E E --> F["Follow-up at 4 weeks"]:::outcome ``` ### Prevention - Keep groin area dry after bathing - Avoid tight clothing and synthetic underwear - Use antifungal powder in high-risk individuals - Avoid sharing towels and personal items