A 30 yr old male came with Redness of skin in groin area due to high friction in summer . Associated with itching. Management and diagnosis.
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tinea cruris intertrigo groin rash
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Diagnosis: Tinea Cruris (Jock Itch / Eczema Marginatum)
This presentation — a 30-year-old male with groin erythema, pruritus, and exacerbation by heat/friction/summer humidity — is classic for tinea cruris, a dermatophyte infection of the groin, genitalia, pubic area, and perineal skin. It is the second most common dermatophytosis worldwide and is 3× more common in men. - Fitzpatrick's Dermatology, p. 2975
Fig. 160-11 Tinea cruris — Fitzpatrick's Dermatology
Etiology
| Organism | Notes |
|---|---|
| Trichophyton rubrum | Most common; extends to pubic, perianal, buttock areas |
| Epidermophyton floccosum | More likely to show central clearing; responsible for epidemics |
| T. mentagrophytes / T. interdigitale | Less common |
Spread: direct contact, fomites, and importantly autoinoculation from tinea pedis (patient picks up infection from feet when putting on underwear). - Andrews' Diseases of the Skin, p. 1997
Clinical Features
- Well-demarcated annular/crescent plaque with a raised, scaly, active advancing border
- Extends from the inguinal fold → inner thighs → may involve perineum/perianal area
- Scrotum typically spared (key distinguishing feature from candidiasis and inverse psoriasis)
- Pruritus prominent; pain if macerated or secondarily infected
- Exacerbated by heat, humidity, tight clothing, and summer season
Differential Diagnosis
| Condition | Distinguishing Features |
|---|---|
| Candidal intertrigo | Moister, brighter red; satellite pustules/papules; involves scrotum; collarette scales |
| Erythrasma (Corynebacterium minutissimum) | Copper-brown color; coral-red fluorescence on Wood's lamp |
| Inverse psoriasis | Well-demarcated; may show serpiginous pustules; look for psoriasis elsewhere; does NOT respond to antifungals |
| Seborrheic dermatitis | Also involves chest, axillae, scalp |
| Contact/irritant dermatitis | History of irritant exposure; no advancing border |
| Lichen simplex chronicus | Lichenification from chronic scratching |
- Fitzpatrick's Dermatology, Table 160-18; Andrews' Diseases of the Skin, p. 2001
Diagnosis
| Test | Finding |
|---|---|
| KOH preparation (scraping from leading edge) | Branching septate hyphae — gold standard, quick office test |
| Fungal culture | Species identification; takes 2–4 weeks |
| Wood's lamp | Negative for tinea cruris (positive coral-red for erythrasma) |
| Skin biopsy | Reserved for diagnostic uncertainty |
Scrape the leading edge of the plaque, not the center. Avoid scraping if patient has already applied topical antifungals — can give false negatives. - Tintinalli's Emergency Medicine, p. 1694
Management
1. Topical Antifungals (First-line for localized disease)
| Drug | Class | Regimen |
|---|---|---|
| Terbinafine 1% cream/gel | Allylamine (fungicidal) | Once daily × 1–2 weeks |
| Clotrimazole 1% cream | Azole | Twice daily × 2–4 weeks |
| Miconazole 2% cream | Azole | Twice daily × 2–4 weeks |
| Ketoconazole 2% cream | Azole | Once–twice daily × 2–4 weeks |
| Econazole 1% cream | Azole (also antibacterial) | Preferred if maceration present |
| Butenafine 1% cream | Allylamine derivative | Once daily × 2 weeks |
Allylamines (terbinafine, naftifine, butenafine) are fungicidal and show superior mycologic cure rates vs. azoles. - Dermatology 2-Volume Set 5e; Katzung Pharmacology 16e
2. Systemic Antifungals (For extensive, recurrent, or refractory disease)
| Drug | Dose | Duration |
|---|---|---|
| Terbinafine 250 mg/day PO | Fewer drug interactions | 2–4 weeks |
| Itraconazole 100 mg/day PO | More drug interactions | 1–6 weeks |
| Fluconazole 150 mg/week PO | Weekly dosing | As per response |
Terbinafine is generally preferred over itraconazole due to fewer drug interactions. - Harrison's Principles of Internal Medicine 22E, p. 1258
3. General / Preventive Measures (Critical for recurrence prevention)
- Keep the area dry: powder application daily (plain talc or antifungal powder)
- Loose-fitting cotton underwear and clothing: reduces friction, heat, and occlusion
- Treat tinea pedis concurrently if present (common co-infection)
- Advise patient to put on socks before underwear to prevent autoinoculation from feet
- Apply a zinc-containing barrier cream to protect skin in the groin fold
- Regular bathing; dry thoroughly after washing
- Avoid sharing towels, clothing
- Fitzpatrick's Dermatology, p. 2976; Andrews' Diseases of the Skin, p. 2003
4. Follow-up
- If no resolution in 4–6 weeks: refer to dermatologist; consider systemic therapy or re-evaluate diagnosis
- Recurrence is common without addressing predisposing factors (tinea pedis, obesity, hyperhidrosis)
Summary Table
| Diagnosis | Tinea cruris (jock itch) |
| Causative organism | T. rubrum, E. floccosum |
| Confirmatory test | KOH prep → branching hyphae |
| First-line Rx | Topical terbinafine or azole × 2–4 weeks |
| Systemic Rx | Oral terbinafine 250 mg/day if extensive |
| Key adjunct | Keep area dry, loose clothing, treat tinea pedis |
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