A 35-year-old female schoolteacher from Delhi presents with a 3-month history of pruritic lesions on her groin and inner thighs. On examination, she has well-demarcated, erythematous, scaly plaques with a raised border and central clearing. The lesions spare the scrotum and are bilateral and symmetrical. KOH mount confirms the presence of septate hyphae. She denies any nail involvement. Which of the following is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Tinea Cruris **Key Point:** Tinea cruris is a **dermatophyte infection of the groin and inner thighs** characterized by well-demarcated, erythematous, scaly plaques with a **raised border and central clearing**. It **characteristically spares the scrotum** — a key distinguishing feature from candidiasis. ### Distinguishing Features: Tinea Cruris vs. Other Inguinal Infections | Feature | Tinea Cruris | Candidiasis | Erythrasma | Pityriasis Versicolor | |---------|--------------|-------------|-----------|----------------------| | **Scrotum involvement** | Spared | Involved | Involved | May be involved | | **Border** | Raised, sharp | Indistinct | Indistinct | Indistinct | | **Scale** | Prominent | Satellite pustules | Minimal | Fine, powdery | | **KOH mount** | Septate hyphae | Budding yeast, pseudohyphae | Gram-positive cocci | Spaghetti and meatballs | | **Organism** | *T. rubrum*, *T. mentagrophytes* | *Candida albicans* | *Corynebacterium minutissimum* | *Malassezia furfur* | | **Symmetry** | Bilateral, symmetrical | Often unilateral | Variable | Bilateral | | **Gender predilection** | Males > Females | Females > Males | Males > Females | Variable | **High-Yield:** In **females**, tinea cruris is less common than in males (due to lower humidity and friction in the groin), but when it occurs, it presents with the same **raised, scaly plaques with central clearing**. The **sparing of the scrotum** is the **cardinal distinguishing feature** from candidiasis. ### Clinical Pearl **Clinical Pearl:** Tinea cruris is often called **"jock itch"** in males. In females, it may extend to the lower abdomen and inner thighs but **never involves the vulva or labia** — if those areas are involved, suspect candidiasis instead. The **bilateral and symmetrical** pattern is typical of tinea cruris. ### Why Scrotum Sparing Occurs The scrotum has a different microenvironment: - Higher moisture and maceration favor *Candida* over dermatophytes - Dermatophytes prefer keratinized epithelium of the thighs and groin folds - Candidiasis thrives in warm, moist, occluded areas **Mnemonic:** **CRURIS = Characteristic raised border, Raised plaques, Unilateral or bilateral, Raised scrotum-sparing, Inflammatory, Symmetrical** [cite:Valia & Valia Dermatology 3e] ## Diagnostic and Management Algorithm ```mermaid flowchart TD A[Pruritic inguinal lesions]:::outcome --> B{Scrotum involved?}:::decision B -->|Yes| C[Suspect Candidiasis]:::outcome B -->|No| D{KOH mount result?}:::decision D -->|Septate hyphae| E[Tinea Cruris]:::outcome D -->|Budding yeast| F[Candidiasis]:::outcome D -->|Spaghetti and meatballs| G[Pityriasis Versicolor]:::outcome E --> H[Topical azole × 2–4 weeks or systemic if extensive]:::action H --> I[Counsel on hygiene, loose clothing, antifungal powder]:::action ```