The FP suspected tinea cruris and asked the patient if he had athlete’s foot. The patient stated that his feet were fine, but the FP asked to examine them anyway and found signs of tinea pedis between the toes (especially in the interspace between toes 4 and 5). While this supported the diagnosis of tinea cruris, the FP decided to confirm his diagnosis with a potassium hydroxide (KOH) preparation. (See video on how to perform a KOH preparation here.) The KOH preparation showed branching hyphae with septate and visible nuclei, confirming the tinea infection.
Tinea cruris is an intensely pruritic superficial fungal infection of the groin and adjacent skin that is more common in men than women and rarely affects children. It is most commonly caused by the dermatophytes Trichophyton rubrum, Epidermophyton floccosum, Trichophyton mentagrophytes, and Trichophyton verrucosum. T rubrum is the most common organism and can be spread by fomites, such as contaminated towels. Autoinoculation can occur from fungus on the feet or hands. Risk factors include obesity and diabetes.
Most topical antifungals can be used to treat tinea cruris, except for nystatin, which only works for Candida. The fungicidal allylamines (naftifine and terbinafine) and butenafine (allylamine derivative) are more convenient, as they allow for a shorter duration of treatment compared with fungistatic azoles (clotrimazole, econazole, ketoconazole, oxiconazole, miconazole, and sulconazole). Topical azoles should be continued for 4 weeks and topical allylamines for 2 weeks or until clinical cure. Fluconazole 150 mg once weekly for 2 to 4 weeks can effectively treat tinea cruris when topical agents are failing. If there are multiple sites infected with fungus, such as the groin and feet, it helps to treat all active areas of infection simultaneously to prevent reinfection of the groin from other body sites.
For this patient, the FP suggested that he buy over-the-counter topical terbinafine to treat the groin and feet twice daily for a minimum of 2 weeks until the fungal infection was no longer visible and symptomatic. At a follow-up visit 4 weeks later, the tinea had resolved and the patient was very happy with the results.
Photos and text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Usatine R, Smith M. Tinea cruris. In: Usatine R, Smith M, Mayeaux EJ, et al, eds. Color Atlas of Family Medicine. 2nd ed. New York, NY: McGraw-Hill; 2013:795-798.
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