Mycotic infections are traditionally divided into two principal groups—superficial and deep. In this chapter, only the superficial infections are discussed: tinea corporis and tinea cruris; dermatophytosis of the feet and dermatophytid of the hands; tinea unguium (onychomycosis); and tinea versicolor. See Chapter 36 for discussion of deep mycoses.
The diagnosis of fungal infections of the skin is based on the location and characteristics of the lesions and on the following laboratory examinations: (1) Direct demonstration of fungi in 10% KOH evaluation of suspected lesions. “If it’s scaly, scrape it” is a time-honored maxim (Figure 6–8) (eFigure 6–21). (2) Cultures of organisms from skin scrapings. (3) Histologic sections of biopsies stained with periodic acid-Schiff technique may be diagnostic if scrapings and cultures are falsely negative.
Branching hyphae at 40× power from a KOH preparation of tinea corporis without using a fungal stain. (Reproduced with permission from Richard P. Usatine, MD, in Usatine RP, Smith MA, Mayeaux EJ Jr, Chumley HS. The Color Atlas and Synopsis of Family Medicine, 3rd ed. McGraw-Hill, 2019.)
KOH preparation of fungus demonstrating pseudohyphae and budding yeast forms. (Reproduced, with permission, from Nicoll D et al. Guide to Diagnostic Tests, 7th ed. McGraw-Hill, 2017.)
A diagnosis should always be confirmed by KOH preparation, culture, or biopsy. Many other diseases cause scaling, and use of an antifungal agent without a firm diagnosis makes subsequent diagnosis more difficult. In general, fungal infections are treated topically except for those with extensive involvement or involving the nails or hair follicles. In these situations, oral agents may be useful, with special attention to their side effects and complications, including hepatic toxicity.
Itraconazole, an azole antifungal, and terbinafine, an allylamine oral antifungal, have excellent activity against dermatophytes. Fluconazole has excellent activity against yeasts and is the treatment of choice for most forms of mucocutaneous candidiasis. Itraconazole, fluconazole, and terbinafine can all cause elevation of liver biochemical tests and—though rarely in the dosing regimens used for the treatment of dermatophytosis—clinical hepatitis. Oral ketoconazole is no longer recommended for the treatment of dermatophytosis (except for tinea versicolor) because of the higher rate of hepatitis.
General Measures & Prevention
Since moist skin favors the growth of fungi, dry the skin carefully after perspiring heavily or after bathing. The use of a hair dryer on a low setting may be helpful. Antifungal or drying powders may be useful with the exception of powders containing corn starch, which may exacerbate fungal infections. The use of topical corticosteroids for other diseases may be complicated by intercurrent tinea or candidal infection, and topical antifungals are often used in intertriginous areas with corticosteroids to prevent this.