Dermatophytoses are caused by fungi (dermatophytes) that infect only superficial keratinized structures (skin, hair, and nails), not deeper tissues. The most important dermatophytes are classified in three genera: Trichophyton, Epidermophyton, and Microsporum. They are spread from infected persons by direct contact. Microsporum is also spread from animals such as dogs and cats. This indicates that to prevent reinfection, the animal must be treated also.

Dermatophytoses (tinea, ringworm) are chronic infections often located in the warm, humid areas of the body (e.g., athlete's foot and jock itch). Typical ringworm lesions have an inflamed circular border containing papules and vesicles surrounding a clear area of relatively normal skin. The lesions are typically pruritic. Broken hairs and dam- aged nails are often seen. The disease is typically named for the affected body part (i.e., tinea capitis [head], tinea corporis [body], tinea cruris [groin], and tinea pedis [foot]) (Figure 1). Tinea unguium, also called onychomycosis, is a disease of the nails, especially toe nails. The nails become thickened, broken, and discolored.

Trichophyton tonsurans is the most common cause of out- breaks of tinea capitis in children and is the main cause of endothrix (inside the hair) infections. Trichophyton rubrum is also a very common cause of tinea capitis. Trichophyton schoenleinii is the cause of favus, a form of tinea capitis in which crusts are seen on the scalp. Trichophyton species also cause an inflammatory pustular lesion on the scalp called a kerion. The marked inflammation is caused by an intense T-cell-mediated reaction to the presence of the fungus.

In some infected persons, hypersensitivity causes dermatophytid ("id") reactions (e.g., vesicles on the fingers). Id lesions are a response to circulating fungal antigens; the lesions do not contain hyphae. Patients with tinea infections show positive skin tests with fungal extracts (e.g., trichophytin).

Scrapings of skin or nail placed in 10% potassium hydroxide (KOH) on a glass slide show septate hypha under microscopy. Cultures on Sabouraud's agar at room temperature develop typical hyphae and conidia. Tinea capitis lesions caused by Microsporum species can be detected by seeing fluorescence when the lesions are exposed to ultraviolet light from a Wood's lamp.

Treatment involves local antifungal creams, such as (terbinafine (Lamisil), undecylenic acid (Desenex), miconazole (Micatin), or tolnaftate (Tinactin). Oral griseofulvin (Fulvicin) or oral itraconazole (Sporanox) can also be used. Tinea unguium can be treated with efinaconazole solution applied topically to the nails. Prevention centers on keeping skin dry and cool.

Fig1. Tinea corporis (ringworm). Note oval, ring-shaped inflamed lesion with central clearing. Caused by dermatophytes such as Epidermophyton, Trichophyton, and Microsporum. (Reproduced with permission from Fauci AS, Braunwald E, Kasper DL et al, eds. Harrison’s Principles of Internal Medicine. 17th ed. New York: McGraw-Hill, 2008. Copyright © 2008 by The McGraw-Hill Companies, Inc.)