A 32-year-old male farmer from rural Maharashtra presents with a 6-week history of pruritic, scaly patches on his groin and inner thighs. The lesions are well-demarcated with raised erythematous borders and central clearing. He reports the condition worsened during the monsoon season. KOH mount of scale shows branching, septate hyphae. What is the most likely causative organism?

## Diagnosis: Tinea Cruris (Jock Itch) ### Clinical Presentation The patient presents with classic features of tinea cruris: - Pruritic, scaly patches in the groin and inner thighs - Well-demarcated borders with central clearing (annular lesion) - Worsening in warm, humid monsoon season - KOH mount showing branching, septate hyphae (confirmatory) ### Causative Organisms in Tinea Cruris | Organism | Prevalence | Geography | Clinical Note | |----------|-----------|-----------|---------------| | **T. rubrum** | Most common (60–70%) | Worldwide, India | Anthropophilic; most frequent in tinea cruris | | T. mentagrophytes | 20–30% | Worldwide | Zoophilic; more common in tinea pedis | | M. canis | Rare in cruris | Worldwide | Zoophilic; more common in tinea corporis | | C. albicans | Not dermatophyte | — | Causes candidiasis, not dermatophytosis | **Key Point:** T. rubrum is the **single most common dermatophyte** causing tinea cruris globally and in India. It is anthropophilic (human-to-human transmission) and thrives in warm, moist intertriginous areas. ### Why T. rubrum? 1. Most common cause of tinea cruris worldwide and in India 2. Anthropophilic — spreads easily in crowded, warm environments 3. Predilection for groin and intertriginous areas 4. Worsens in monsoon (humidity favors growth) **High-Yield:** T. rubrum accounts for >60% of all dermatophyte infections in India, particularly tinea cruris and tinea corporis. [cite:Inamadar & Palit, Indian Dermatology Online Journal] **Clinical Pearl:** Tinea cruris typically spares the scrotum (unlike candidiasis), which is a useful clinical discriminator.