A 34-year-old female office worker from Bangalore presents with a 6-week history of scaling, erythema, and pruritus on the dorsal surfaces of both hands and fingers, with relative sparing of the palms. She reports the rash began after increased hand washing due to occupational stress. Examination shows well-demarcated plaques with fine scale and a raised, active border. KOH preparation demonstrates branching septate hyphae. What is the most likely diagnosis?

Explanation

## Diagnosis: Tinea Manuum (Dry Type) — Dorsal Hand Variant ### Clinical Presentation **Key Point:** Tinea manuum refers to dermatophyte infection of the hand. The "dry type" presents with well-demarcated erythematous plaques, fine scale, and a raised active border — confirmed by KOH demonstration of branching septate hyphae. Dorsal hand involvement with relative palmar sparing is a recognized presentation of tinea manuum. ### Why Tinea Manuum, Not Tinea Corporis? **High-Yield:** Tinea corporis is defined as dermatophyte infection of the **glabrous (smooth) skin of the trunk and extremities, excluding the hands, feet, groin, face, and scalp**. When dermatophyte infection occurs specifically on the **hand** (dorsal or palmar surface), the correct site-specific diagnosis is **tinea manuum** — regardless of whether the palms are involved. - The stem explicitly localizes the infection to the **dorsal surfaces of both hands and fingers** — this is the hand, making tinea manuum the correct anatomical designation. - Tinea corporis would be appropriate if the plaques were on the forearm, trunk, or other non-hand glabrous skin. - The "dry type" of tinea manuum classically shows diffuse palmar scaling, but dorsal hand involvement with fine scale and raised borders is also well-described and falls under the tinea manuum umbrella. ### Differential Diagnosis Table | Feature | Tinea Manuum (Dry) | Tinea Corporis | Dyshidrotic Eczema | Contact Dermatitis | |---------|-------------------|---------------|-------------------|-------------------| | **Location** | Hand (dorsal/palmar) | Trunk/extremities (not hand) | Palms/soles | Variable | | **Border** | Raised, active | Raised, active | Ill-defined | Ill-defined | | **Scale** | Fine to diffuse | Fine | Vesicles → scale | Variable | | **KOH mount** | Positive | Positive | Negative | Negative | | **Pruritus** | Mild–moderate | Moderate | Intense | Moderate–intense | ### Key Distinguishing Features **Clinical Pearl:** The anatomical site determines the tinea subtype. Infection on the **hand** = tinea manuum; infection on the **foot** = tinea pedis; infection on the **groin** = tinea cruris; infection on the **trunk/extremities (excluding hands/feet/groin/face/scalp)** = tinea corporis. This is a classic NEET PG distinction. **Warning:** Dyshidrotic eczema presents with **vesicles** (not plaques), intense pruritus, and a **negative KOH mount**. Contact dermatitis lacks a raised active border and is KOH-negative. Neither would show hyphae on KOH preparation. ### Causative Organisms - *Trichophyton rubrum* (most common, ~70%) - *Trichophyton mentagrophytes* - *Epidermophyton floccosum* ### Management 1. **Topical antifungals** (terbinafine, clotrimazole, miconazole) for 2–4 weeks for localized disease 2. **Oral terbinafine** (250 mg daily × 2–4 weeks) for extensive, bilateral, or recurrent cases 3. **Hygiene:** Keep hands dry; avoid prolonged water exposure; antifungal powder as adjunct 4. **Avoid topical corticosteroids** alone — worsens fungal infection (tinea incognito) [cite: Andrews' Diseases of the Skin, 13e; Fitzpatrick's Dermatology, 9e; KD Tripathi Essentials of Medical Pharmacology]