Mixed diagnoses – 10 cases (3 of 11)

This is tinea cruris. Acceptable synonyms include tinea inguinalis, groin dermatophytosis, ringworm of the groin, gym itch, eczema marginatum, dhobie itch, jock itch and crotch rot!

Tinea cruris presents as slowly expanding areas of erythema with central clearing centred on the inguinal creases and extending down the medial aspects of the thighs and upwards onto the lower abdomen. There is a scaly circinate border. Postinflammatory pigmentation is common in darker skinned individuals, and secondary excoriation and lichenification are common.

It is a contagious infection transmitted by fomites such as contaminated towels, or by autoinoculation from the hands or feet (tinea manuum, tinea pedis, tinea unguium). Risk factors for initial infection or reinfection include wearing tight-fitting or wet underwear.

Take scrapings from the scaly border for mycology, together with a blue-topped swab for bacterial culture. As half of those with tinea cruris also have tinea pedis, examine the feet and toenails and take scrapings and clippings from these sites as well.

The differential diagnosis includes other reasons for intertrigo, most commonly irritant dermatitis (chafing, obesity), candida (acute flare with satellite papules and pustules), erythrasma (relatively asymptomatic) and psoriasis (symmetrical, sharply demarcated and diffusely shiny red).

This depends on the severity and extent of the disorder. Mild tinea cruris will respond to topical imidazoles or terbinafine. An oral agent (terbinafine, itraconazole or fluconazole) is indicated for more severe disease. The duration depends whether the toenails are the reservoir of infection; if so, a three-month course is required with follow-up to ensure clinical and mycological cure.