Tinea cruris is a dermatophytosis Overview of Dermatophytoses Dermatophytoses are fungal infections of keratin in the skin and nails (nail infection is called tinea unguium or onychomycosis). Symptoms and signs vary by site of infection. Diagnosis is by... read more that is commonly caused by Trichophyton rubrum or T. mentagrophytes. The primary risk factors are associated with a moist environment (ie, warm weather, wet and restrictive clothing, obesity causing constant apposition of skinfolds). Men are affected more than women because of apposition of the scrotum and thigh.
Typically, a pruritic, ringed lesion extends from the crural fold over the adjacent upper inner thigh. Infection may be bilateral. Lesions may be complicated by maceration, miliaria, secondary bacterial or candidal infection, and reactions to treatment. In addition, scratch dermatitis and lichenification can occur. Recurrence is common because fungi may repeatedly infect susceptible people or people with onychomycosis Onychomycosis Onychomycosis is fungal infection of the nail plate, nail bed, or both. The nails typically are deformed and discolored white or yellow. Diagnosis is by appearance, wet mount, culture, polymerase... read more 
or tinea pedis Tinea Pedis (Athlete's Foot) Tinea pedis is a dermatophyte infection of the feet. Diagnosis is by clinical appearance and sometimes by potassium hydroxide wet mount, particularly if the infection manifests as hyperkeratotic... read more 
, which can serve as a dermatophyte reservoir. Flare-ups occur more often during summer.
Diagnosis of Tinea Cruris
Clinical evaluation
Potassium hydroxide wet mount
Scrotal involvement is usually absent or slight; by contrast, the scrotum is often inflamed in candidal intertrigo or lichen simplex chronicus. If the appearance is not diagnostic, a potassium hydroxide wet mount is helpful.
Differential diagnosis of tinea cruris includes
Treatment of Tinea Cruris
Topical antifungal cream, lotion, or gel
(See table: Options for Treatment of Superficial Fungal Infections* Options for Treatment of Superficial Fungal Infections* Candidiasis is skin and mucous membrane infection with Candida species, most commonly Candida albicans. Infections can occur anywhere and are most common in skinfolds, digital web spaces, genitals... read more 
.)
Antifungal choices include terbinafine, miconazole, clotrimazole, ketoconazole, econazole, naftifine, and (uncommonly) ciclopirox applied 2 times a day for 10 to 14 days.
Itraconazole 200 mg orally once a day or terbinafine 250 mg orally once a day for 3 to 6 weeks may be needed in patients who have refractory, inflammatory, or widespread infections.
Key Points
Suspect tinea cruris when pruritic, ringed lesions extend from the crural fold over the adjacent upper inner thigh, particularly in obese patients or men.
Topical terbinafine, miconazole, clotrimazole, ketoconazole, econazole, or naftifine 2 times a day for 10 to 14 days is usually effective.
