Dermatophyte Infections -- American Family Physician

Dermatophytoses Because dermatophytes require keratin for growth, they are restricted to hair, nails, and superficial skin. Thus, these fungi do not infect mucosal surfaces. Dermatophytoses are referred to as “tinea” infections. They are also named for the body site involved. Some dermatophytes are spread directly from one person to another (anthropophilic organisms). Others live in and are transmitted to humans from soil (geophilic organisms), and still others spread to humans from animal hosts (zoophilic organisms). Transmission of dermatophytes also can occur indirectly from fomites (e.g., upholstery, hairbrushes, hats). Anthropophilic organisms are responsible for most fungal skin infections. Transmission can occur by direct contact or from exposure to desquamated cells. Direct inoculation through breaks in the skin occurs more often in persons with depressed cell-mediated immunity. Once fungi enter the skin, they germinate and invade the superficial skin layers. In patients with dermatophytoses, physical examination may reveal a characteristic T he dryness of the skin’s outer layer discourages colonization by microorganisms, and the shedding of epidermal cells keeps many microbes from establishing residence. However, the skin’s mechanisms of protection may fail because of trauma, irritation, or maceration. Furthermore, occlusion of the skin with nonporous materials can interfere with the skin’s barrier function by increasing local temperature and hydration. With inhibition or failure of the skin’s protective mechanisms, cutaneous infection may occur. Microsporum, Trichophyton, and Epidermophyton species are the most common pathogens in skin infections. Less frequently, superficial skin infections are caused by nondermatophyte fungi (e.g., Malassezia furfur in tinea [pityriasis] versicolor) and Candida species. This article reviews the diagnosis Dermatophytes are fungi that require keratin for growth. These fungi can cause superficial infections of the skin, hair, and nails. Dermatophytes are spread by direct contact from other people (anthropophilic organisms), animals (zoophilic organisms), and soil (geophilic organisms), as well as indirectly from fomites. Dermatophyte infections can be readily diagnosed based on the history, physical examination, and potassium hydroxide (KOH) microscopy. Diagnosis occasionally requires Wood’s lamp examination and fungal culture or histologic examination. Topical therapy is used for most dermatophyte infections. Cure rates are higher and treatment courses are shorter with topical fungicidal allylamines than with fungistatic azoles. Oral therapy is preferred for tinea capitis, tinea barbae, and onychomycosis. Orally administered griseofulvin remains the standard treatment for tinea capitis. Topical treatment of onychomycosis with ciclopirox nail lacquer has a low cure rate. For onychomycosis, “pulse” oral therapy with the newer imidazoles (itraconazole or fluconazole) or allylamines (terbinafine) is considerably less expensive than continuous treatment but has a somewhat lower mycologic cure rate. The diagnosis of onychomycosis should be confirmed by KOH microscopy, culture, or histologic examination before therapy is initiated, because of the expense, duration, and potential adverse effects of treatment. (Am Fam Physician 2003;67:101-8. Copyright© 2003 American Academy of Family Physicians.)