A 59-year-old man presents with itching in the groin (Figure 139-1). On examination, he was found to have scaly erythematous plaques in the inguinal area. A skin scraping was treated with Swartz-Lamkins stain and the dermatophyte was highly visible under the microscope (Figure 139-2). 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. (Courtesy of 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. (Courtesy of Richard P. Usatine, MD.)
Tinea cruris is an intensely pruritic superficial fungal infection of the groin and adjacent skin.
Crotch rot and jock itch.
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 139-3 and 139-4). Occasionally, tinea cruris may show central sparing with an annular pattern as in Figure 139-5, but most often is homogeneously distributed as in Figures 139-3 and 139-4.
Tinea cruris in an older black man with hyperpigmentation secondary to the inflammatory response. A silvery scale is also seen and psoriasis should be considered in the differential diagnosis. In such a case, performing a potassium hydroxide preparation is crucial to making an accurate diagnosis as it is not possible to know the diagnosis by appearance only. (Courtesy of Richard P. Usatine, MD.)
Tinea cruris that has expanded beyond the inguinal area in this 35-year-old black man. Postinflammatory hyperpigmentation is visible throughout the infected area. (Courtesy of Richard P. Usatine, MD.)
An 18-year-old woman with tinea cruris showing erythema and scale in an annular pattern. Central clearing is less common in tinea cruris than tinea corporis but can occur. (Courtesy of Richard P. Usatine, MD.)
By definition tinea cruris is in the inguinal area. However, the fungus can grow outside of this area to involve the abdomen and thighs (Figures 139-4 and 139-6). Tinea can be present in multiple locations, as in the patient in Figure 139-7 who had tinea in the groin, on her feet and face, and under her breasts.
A 54-year-old man with tinea cruris and corporis for decades despite multiple treatments with oral antifungal medications. His cultures show T. rubrum sensitive to all the typical oral antifungal medications, but his tinea never completely clears. He does not have a known immunodeficiency but his immune system appears not to recognize the T. rubrum as foreign. (Courtesy of Richard P. Usatine, MD.)
A 55-year-old woman with tinea cruris showing erythema and scale. Although less common in women, women do get tinea cruris. This patient had tinea on her feet, face, and under her breasts. She was treated with oral terbinafine for 3 weeks. (Courtesy of Richard P. Usatine, MD.)
Diagnosis is often made based on clinical presentation, but a skin scraping treated with KOH and a fungal stain analyzed under the microscope can be helpful (Figure 139-2). False negatives may occur if scraping is inadequate, patient is using topical antifungals, or the viewer is inexperienced.
Skin scraping and culture is definitive but expensive, and may take up to 2 weeks for the culture to grow.
UV lamp can be used to look for the coral red fluorescence of erythrasma (see Chapter 119, Erythrasma). Most tinea cruris is caused by T. rubrum so will not fluoresce.