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INTRODUCTION TO CHAPTER

Most superficial fungal infections of the skin are caused by dermatophytes or yeasts. They rarely cause serious illness, but fungal infections are often recurrent or chronic in otherwise healthy people. The availability of effective over-the-counter antifungal medications has been helpful to people with actual fungal infections, but these medications are frequently used by people who actually have other skin diseases such as dermatitis. One of the main diagnostic problems with fungal infections is that they closely resemble dermatitis and other inflammatory disorders. Both clinicians and patients overdiagnose and underdiagnose fungal infections. A few simple clinical points can help avoid misdiagnoses:

  • Many inflammatory skin diseases such as nummular dermatitis present with an annular pattern and are often misdiagnosed as tinea corporis.

  • Dermatitis and dermatophyte infections on the feet have a very similar appearance. However, the presence of toe web scale and nail plate thickening is more characteristic of a fungal infection.

  • Half of all nail disorders are caused by fungus. The other causes of nail diseases such as psoriasis and lichen planus may appear very similar to fungal infections.

  • Fungal infections are rare on the hands, but when they do occur they are almost indistinguishable from irritant contact dermatitis or dry skin.

  • Fungal infections on the scalp are rare after puberty.

  • The diagnosis of a suspected fungal skin infection should be confirmed with a potassium hydroxide (KOH) examination or fungal culture.

INTRODUCTION TO DERMATOPHYTE INFECTIONS

Dermatophytes can penetrate and digest keratin present in the stratum corneum of the epidermis, hair, and nails. Superficial dermatophyte infections are a common cause of skin disease worldwide, especially in tropical areas. The names of the various dermatophyte infections begin with "tinea," which is a Latin term for "worm." The second word in the name is the Latin term for the affected body site:

  • Tinea capitis—scalp

  • Tinea barbae—beard

  • Tinea faciei—face

  • Tinea corporis—trunk and extremities

  • Tinea manuum—hands

  • Tinea cruris—groin

  • Tinea pedis—feet

  • Tinea unguium (onychomycosis)—nails

Three dermatophyte genera and 9 species are responsible for most infections in North America and Europe.

  • Trichophyton: rubrum, tonsurans, mentagrophytes, verrucosum, and schoenlenii

  • Microsporum: canis, audouinii, and gypseum

  • Epidermophyton: floccosum

The species within these genera may be further classified according to their host preferences:

  • Anthropophilic—human

  • Zoophilic—animal

  • Geophilic—soil

Infections can occur by direct contact with infected hosts or fomites.

Dermatophyte infections can mimic many common skin rashes. Therefore, it is important to confirm the diagnosis of a suspected fungal infection with a microscopic examination using KOH or with cultures.

Proper specimen collection is very important (Table 4-1). False-negative results can occur when specimens are taken from the wrong site or when insufficient volume is collected or when the patient has been using antifungal medications.

Most dermatophyte infections can be confirmed by performing a KOH examination ...

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