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Overview of Dermatophytoses
Dermatophytoses are fungal infections of keratin in the skin and nails (nail infection is called tinea unguium or onychomycosis—see Onychomycosis). Symptoms and signs vary by site of infection. Diagnosis is by clinical appearance and by examination of skin scrapings on potassium hydroxide wet mount. Treatment varies by site but always involves topical or oral antifungals.
Dermatophytes are molds that require keratin for nutrition and must live on stratum corneum, hair, or nails to survive. Human infections are caused by Epidermophyton, Microsporum, and Trichophyton spp. These infections differ from candidiasis in that they are rarely if ever invasive. Transmission is person-to-person, animal-to-person, and, rarely, soil-to-person. The organism may persist indefinitely. Most people do not develop clinical infection; those who do may have impaired T-cell responses from an alteration in local defenses (eg, from trauma with vascular compromise) or from primary (hereditary) or secondary (eg, diabetes, HIV) immunosuppression.
Symptoms and signs vary by site (skin, hair, nails). Organism virulence and host susceptibility and hypersensitivity determine severity. Most often, there is little or no inflammation; asymptomatic or mildly itching lesions with a scaling, slightly raised border remit and recur intermittently. Occasionally, inflammation is more severe and manifests as sudden vesicular or bullous disease (usually of the foot) or as an inflamed boggy lesion of the scalp (kerion).
Diagnosis is based on clinical appearance and site of infection and can be confirmed by skin scrapings and demonstration of hyphae on potassium hydroxide (KOH) wet mount or by culture of plucked hairs. For onychomycosis, the most sensitive test is a periodic acid-Schiff stain of nail clippings. For KOH wet mount, the affected area of the nail plate, not subungual debris, should be pared and tested. Identification of specific organisms by culture is unnecessary except for scalp infection (where an animal source may be identified and treated) and nail infection (which may be caused by a nondermatophyte). Culture may also be useful when overlying inflammation and bacterial infection are severe and/or accompanied by alopecia.
Differential diagnosis includes
Topical antifungals are generally adequate (see Options for Treatment of Superficial Fungal Infections*). OTC terbinafine is fungicidal and allows for shorter treatment duration. Econazole or ciclopirox may be better if candidal infection cannot be excluded. Other adequate OTC topical treatments include clotrimazole and miconazole. Oral antifungals are used for most nail and scalp infections, resistant skin infections, and patients unwilling or unable to adhere to prolonged topical regimens; doses and duration differ by site of infection.
Corticosteroids are sometimes used in addition to antifungal creams to help relieve itching and inflammation. However, combining topical corticosteroids and antifungal creams should be avoided when possible because topical corticosteroids promote fungus growth. Commercially available topical corticosteroid and antifungal products should not be used as substitutes for obtaining an accurate diagnosis with a KOH wet mount or culture.
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