A 59-year-old man presents with itching in the groin (Figure 145-1). On examination, he was found to have scaly erythematous plaques in the inguinal area. A KOH preparation was performed with Swartz Lamkins stain, and the dermatophyte was highly visible under the microscope (Figure 145-2). He was treated with a topical antifungal medicine until his tinea cruris resolved.
Tinea cruris in a 59-year-old Hispanic man present for 1 year. (Reproduced with permission from Richard P. Usatine, MD.)
Microscopic view of the scraping of the groin in a man with tinea cruris. The hyphae are easy to see under 40× power with Swartz Lamkins stain. (Reproduced with permission from Richard P. Usatine, MD.)
Tinea cruris is a pruritic superficial infection of the groin and adjacent skin caused by a dermatophyte fungus.
Common names: Crotch rot and jock itch.
It is estimated that 10% to 20% of the world population is affected by fungal skin infections.1
Dermatophytes are the most prevalent agents causing fungal infections of the skin.2
Trichophyton rubrum causes the majority of cases of tinea cruris.2
Tinea cruris is more common in men than women (threefold) and rare in children.
ETIOLOGY AND PATHOPHYSIOLOGY
Caused by the dermatophytes Trichophyton rubrum, Epidermophyton floccosum, Trichophyton mentagrophytes, and Trichophyton verrucosum.
Can be spread by fomites, such as contaminated towels.
The dermatophytes release keratinases, which allow invasion of the cornified cell layer of the epidermis.
Autoinoculation can occur from fungus on the feet or hands.
Wearing tight-fitting or wet clothing or underwear has traditionally been suggested; however, in a study of Italian soldiers, none of the risk factors analyzed (e.g., hyperhidrosis, swimming pool attendance) were significantly associated with any fungal infection.3
Obesity and diabetes mellitus may be risk factors.4
The cardinal features are scale and signs of inflammation. In light-skinned persons inflammation often appears pink or red, and in dark-skinned persons the inflammation often leads to hyperpigmentation (Figures 145-3 and 145-4). Occasionally, tinea cruris may show central sparing with an annular pattern as in Figure 145-5, but most often is homogeneously distributed as in Figures 145-3 and 145-4.
Tinea cruris and tinea corporis in a Hispanic man with hyperpigmentation secondary to the inflammatory response. KOH positive. (Reproduced with permission from Richard P. Usatine, MD.)