What is tinea cruris?
Tinea cruris (or jock itch) is a dermatophytosis (fungal infection) of the groin commonly caused by Trichophyton rubrum. Other frequent causes are T. mentagrophytes and E. floccosum. These fungus tend to grow in moist environments, like warm wet skin folds at the groins and between the toes. For this reason, tinea cruris is more commonly seen in men. Other risk factors include excessive sweating, obesity, diabetes and immunocompromised. In order to prevent further spread of the fungal infection, tinea cruris treatment should be given promptly.
What are the symptoms of tinea cruris?
Tinea cruris typically starts with a red patch on the upper inner thigh. The infection then spread outwardly, forming ring-like lesions with clear skin in the center. These lesions are also red, slightly raised and have clear demarcations. Patients often complain of itchiness and skin macerations. The infection may be at both left and right sides, and may spread to the surrounding skin such as the perineum, areas around the anus, or the buttocks. Fortunately, the scrotum is often not affected by the infection. Additionally, patients may develop complications such as scratch dermatitis, lichenification (hard, thickened skin), miliaria (blocked sweat glands), and secondary bacterial or candidiasis infection. People with coexisting infection of tinea pedis (fungal infection at the toes) or onychomycosis (fungal infection at the nail) are more easily infected with tinea cruris. As these fungus favour warm weather, the infection may flare up during the summer season.
How is tinea cruris diagnosed?
Diagnosis is made by clinical appearance of the rash and potassium hydroxide wet mount. During examination, potassium hydroxide added on to the scales obtained from the fungal infection will show evidence of fungus, which has a characteristic segmented hyphae. In order to get the best result, doctors will obtain skin samples by scraping at the border of the ring lesions. Dermatophyte test medium and fungal cultures are other possible ways to confirm the diagnosis. Involvement of the scrotums might suggest a differential diagnosis of candidal intertrigo or lichen simplex chronicus. The potassium hydroxide wet mount test can help to exclude other common skin disorders that present with red patches in the groin area, namely inverse psoriasis, erythrasma and seborrheic dermatitis.
What are the treatments of tinea cruris?
Tinea cruris is best treated with topical antifungal agents such as azoles, allylamines, butenafine, tolnaftate and ciclopirox. All of these have been found to be effective against dermatophyte infections. In contrast, nystatin which is effective for candidiasis, is not effective for dermatophytes. The topical antifungals are usually applied twice daily for 10 to 14 days until complete resolution is achieved. If the topical medications fail to resolve the infection, or if the patients have more widespread lesions, then oral antifungal drugs can be given. Common medications include terbinafine and itraconazole. Dosage of terbinafine is 250mg daily for 1 to 2 weeks while itraconazole is 200mg daily for 1 week. Other oral antifungals are fluconazole and griseofulvin, but they require a longer course up to 4 weeks.
It is very common for tinea cruris to recur due to the high possibility of simultaneous presence of more than one type of fungal infection. Hence, doctors should not only treat current fungal infection at the groin, but also do a full-body check to identify and treat other coexisting fungal infections, particularly at the nails, feet and body. Patients are encouraged to practice good hygiene, reduce body weight and control diabetes (if any) in order to prevent re-infection. Helpful practices include using desiccant powders daily in the groin area to keep skin dry, and avoid tight-fitting trousers. Go for cotton-made underwears which keep skin well ventilated (airy and not moist).