A 28-year-old male farmer from Punjab presents with a 3-week history of itching and scaling on the inner thighs and scrotum. He reports increased sweating due to his occupation and wears tight jeans. Examination reveals well-demarcated, erythematous plaques with central clearing and a raised, scaly border. KOH mount shows branching septate hyphae. What is the most likely diagnosis?

Explanation

## Diagnosis: Tinea Cruris **Key Point:** Tinea cruris ("jock itch") is a dermatophyte infection of the groin, inner thighs, and scrotum, classically presenting with well-demarcated erythematous plaques with central clearing and a raised, scaly border. ### Clinical Features of Tinea Cruris | Feature | Details | |---------|----------| | **Site** | Groin, inner thighs, scrotum, perianal area (spares scrotum in early stages) | | **Appearance** | Erythematous, scaly plaques with raised border; central clearing common | | **Symptoms** | Intense pruritus, burning sensation | | **Risk factors** | Male > female (4:1); warm, moist environment; tight clothing; poor hygiene | | **Causative agents** | *Trichophyton rubrum* (most common), *T. mentagrophytes*, *Epidermophyton floccosum* | | **KOH mount** | Branching septate hyphae | **High-Yield:** Tinea cruris is predominantly a male infection due to anatomical factors (scrotum creates warm, moist microenvironment) and is exacerbated by occlusive clothing and sweating — exactly the scenario in this farmer. ### Differential Diagnosis | Condition | Key Distinguishing Feature | |-----------|---------------------------| | **Tinea corporis** | Affects trunk, limbs, face; not limited to groin; less likely to spare scrotum | | **Candidiasis** | Satellite pustules beyond border; white exudate; KOH shows budding yeast (not septate hyphae); more common in immunocompromised | | **Erythrasma** | Non-scaly, well-demarcated brown-red macules; coral-red fluorescence on Wood's lamp; caused by *Corynebacterium minutissimum* (not fungal) | **Clinical Pearl:** The combination of groin location, scrotum involvement, well-demarcated border with central clearing, and septate hyphae on KOH is pathognomonic for tinea cruris. **Mnemonic:** **CRURIS** — **C**old-weather risk (moisture), **R**aised border, **U**nder scrotum, **R**ubrum (most common), **I**tchy, **S**caly. ### Management - Topical azoles (miconazole, clotrimazole) for 2–4 weeks - Systemic terbinafine (250 mg daily for 2–4 weeks) if extensive or resistant - Hygiene: keep area dry, avoid occlusive clothing, antifungal powder