Tinea Cruris

Tinea cruris is a dermatophyte infection of the groin, proximal medial thighs, pubic region, perineum and buttocks. It is also called jock itch. It is common in adolescent and adult men, much less common in women, and rare in prepubertal children. Occlusion, heat and sweating drive the pattern, so it is more frequent in tropical climates, in summer and in athletes.

Infection is confined to the stratum corneum. The scrotum is characteristically spared, which has diagnostic value.

The commonest route is autoinoculation from the feet and nails, through socks and underwear pulled over infected feet. Other routes are shared towels and clothing, contaminated floors and mats, and sexual contact.

Risk factors: obesity and deep skin folds, tight or occlusive clothing, sweating, diabetes mellitus, topical or systemic corticosteroids, immunosuppression, coexisting tinea pedis or onychomycosis, and male sex.

Hyphae spread outward in the stratum corneum from the crural fold, producing an advancing active edge with central clearing. The scrotum is usually spared because its temperature, moisture and surface lipid composition differ from the adjacent thigh skin. Chronic scratching causes lichenification and post inflammatory hyperpigmentation. Topical corticosteroids, including combined steroid antifungal creams, suppress the edge and scale, increase spread and produce tinea incognito.

• Sharply marginated, erythematous to brown plaques extending from the crural fold onto the medial upper thighs, with a raised, scaly, sometimes vesicular active edge and relative central clearing.
• Extension to the buttocks, pubic region, lower abdomen and perineum in prolonged disease.
• Itch of variable severity, and burning when the skin is macerated.
• Chronic infection with Trichophyton rubrum gives dry, scaly, hyperpigmented, lichenified plaques with follicular papules.
• Inflammatory forms with pustules and follicular involvement indicate deeper follicular infection (Majocchi granuloma).
• Women: involvement of the groin folds and pubic region, often in the setting of obesity and tinea pedis.
• Pubogenital disease from genotype VII: inflamed plaques, pustules and erosions on the pubic area, genital skin and thighs, sometimes with painful lymphadenopathy.
• Tinea incognito: indistinct edge, reduced scale, follicular papules and pustules.

Complications are secondary bacterial infection, lichen simplex chronicus, permanent pigment change, and Majocchi granuloma.

A groin eruption that does not clear with an adequate antifungal course needs a biopsy.

• Specimen: scale scraped from the active edge with a blade, after cleaning the skin with 70 percent alcohol. Scale from the centre of the lesion often contains no organisms.
• Potassium hydroxide preparation (10 to 20 percent): septate, branching hyphae of uniform width, sometimes with arthroconidia in chains. Calcofluor white increases sensitivity. Budding yeasts and pseudohyphae indicate Candida.
• Culture: Sabouraud dextrose agar with chloramphenicol and cycloheximide at 25 to 30 degrees Celsius, held for 3 to 4 weeks. Indicated for extensive, recurrent or treatment resistant disease, before oral therapy, and when pubogenital infection or resistance is suspected.
• Sequencing and susceptibility work: needed to identify Trichophyton indotineae and Trichophyton mentagrophytes genotype VII, and for squalene epoxidase gene analysis where terbinafine failure is suspected.
• Wood lamp: coral red fluorescence points to erythrasma, and dermatophytes do not fluoresce in skin.
• Pubogenital disease: screening for other sexually transmitted infections is added, and sexual partners are examined.

Topical therapy suffices for localised disease. The drug is applied to the lesion and to 2 cm of surrounding skin, and is continued for 1 to 2 weeks after clearance to reduce relapse. Feet and nails are examined and treated at the same time, because untreated tinea pedis reseeds the groin.

Groin skin is thin and occluded, so potent topical corticosteroids cause atrophy and striae and are avoided. Combined corticosteroid antifungal creams are avoided. Itch is controlled with an oral antihistamine. Macerated skin is kept dry with an antifungal or absorbent powder after treatment.

Oral therapy is for extensive disease, folliculitic or inflammatory disease, chronic Trichophyton rubrum infection, immunosuppressed patients, and failure of topical therapy.

Drug safety limits are those of the agents themselves: terbinafine is avoided in active liver disease and when creatinine clearance is below 50 mL per minute; itraconazole is a strong CYP3A4 inhibitor and is avoided in heart failure; fluconazole is halved when creatinine clearance is below 50 mL per minute; griseofulvin is contraindicated in pregnancy, porphyria and hepatocellular failure.

Terbinafine resistant disease (Trichophyton indotineae): itraconazole 200 mg daily for at least 4 weeks, usually 6 to 8 weeks or until clinical and mycological clearance, with a topical azole or ciclopirox as adjunct. Relapse is frequent, and household and sexual contacts are examined.

Pubogenital infection: oral terbinafine 250 mg once daily or itraconazole 200 mg once daily, for 2 to 4 weeks and longer if the response is slow. Partners are examined and treated, and sexual contact is avoided until cure.

• Treat tinea pedis and onychomycosis in the same course.
• Put on socks before underwear to avoid dragging fungus from the feet to the groin.
• Wear loose, absorbent cotton clothing, dry the groin thoroughly after bathing and exercise, and change out of sweaty clothes promptly.
• Wash towels, underwear and athletic supporters in hot water, and do not share them.
• Reduce weight and optimise glycaemic control where relevant.
• Use an antifungal or absorbent powder during warm months in recurrent disease.