Fast Five Quiz: Embarrassing Medical Conditions

George D. Harris, MD, MS


June 27, 2019

Clinical cure of an uncomplicated tinea cruris infection usually can be achieved using topical antifungal agents of the imidazole or allylamine family. Consider patients unable to use topical treatments consistently or with extensive or recalcitrant infection as candidates for systemic administration of antifungal therapy, which has been proven safe in immunocompetent persons.

Prevention of tinea cruris reinfection is an essential component of disease management. Patients with tinea cruris often have concurrent dermatophyte infections of the feet and hands. Treat all active areas of tinea cruris infection simultaneously to prevent reinfection of the groin from other body sites. Advise patients with tinea pedis to put on their socks before their undershorts to reduce the possibility of direct contamination. Advise patients with tinea cruris to dry the crural folds completely after bathing and to use separate towels for drying the groin and other parts of the body.

Tinea cruris is a contagious infection transmitted by fomites, such as contaminated towels or hotel bedroom sheets, or by autoinoculation from a reservoir on the hands or feet (tinea manuum, tinea pedis, tinea unguium). The etiologic agents in tinea cruris produce keratinases, which allow invasion of the cornified cell layer of the epidermis. The host immune response may prevent deeper invasion. The most common etiologic agents for tinea cruris include Trichophyton rubrum and Epidermophyton floccosum; less commonly, Trichophyton mentagrophytes and Trichophyton verrucosum are involved.

The penis and scrotum typically are spared in tinea cruris; however, the infection may extend to the perineum and buttocks. Large patches of erythema with central clearing are centered on the inguinal creases and extend distally down the medial aspects of the thighs and proximally to the lower abdomen and pubic area. Scale is demarcated sharply at the periphery. In acute tinea cruris infections, the rash may be moist and exudative. Chronic infections typically are dry with a papular annular or arciform border and barely perceptible scale at the margin. Central areas are typically hyperpigmented and contain a scattering of erythematous papules and a little scale.

Microscopic examination of a KOH wet mount of scales is diagnostic in tinea cruris. The procedure for KOH wet mount is as follows:

  • Clean the area with 70% alcohol.

  • Collect scales from the margin of the lesion; use a scalpel or the edge of a glass slide for this purpose. Cover the collected scales with a cover slip; allow a drop of KOH (10%-15% wt/vol) to run under the cover slip.

  • The keratin and debris should dissolve after a few minutes. The process can be hastened by heating the slide or by the addition of a keratolytic or dimethyl sulfoxide to the KOH formulation.

  • The addition of one drop of lactophenol cotton blue solution to the wet-mount preparation heightens the contrast and aids in the diagnosis.

  • Negative results on KOH preparation do not exclude fungal infection.

  • Scale culture is useful for fungal identification but is a more specific, albeit less sensitive, diagnostic test than KOH wet mount.

Read more on tinea cruris.


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