Cutaneous Fungal Infections

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Chapter 658 Cutaneous Fungal Infections

Tinea Versicolor

A common, innocuous, chronic fungal infection of the stratum corneum, tinea versicolor is caused by the dimorphic yeast Malassezia globosa. The synonyms Pityrosporum ovale and Pityrosporum orbiculare were used previously to identify the causal organism.

Dermatophytoses

Dermatophytoses are caused by a group of closely related filamentous fungi with a propensity for invading the stratum corneum, hair, and nails. The 3 principal genera responsible for infections are Trichophyton, Microsporum, and Epidermophyton.

Epidemiology

Host defense has an important influence on the severity of the infection. Disease tends to be more severe in individuals with diabetes mellitus, lymphoid malignancies, immunosuppression, and states with high plasma cortisol levels, such as Cushing syndrome. Some dermatophytes, most notably the zoophilic species, tend to elicit more severe, suppurative inflammation in humans. Some degree of resistance to re-infection is acquired by most infected persons and may be associated with a delayed hypersensitivity response. No relationship has been demonstrated, however, between antibody levels and resistance to infection. The frequency and severity of infection are also affected by the geographic locale, the genetic susceptibility of the host, and the virulence of the strain of dermatophyte. Additional local factors that predispose to infection include trauma to the skin, hydration of the skin with maceration, occlusion, and elevated temperature.

Occasionally, a secondary skin eruption, referred to as a dermatophytid or “id” reaction, appears in sensitized individuals and has been attributed to circulating fungal antigens derived from the primary infection. The eruption is characterized by grouped papules (Fig. 658-2) and vesicles and, occasionally, by sterile pustules. Symmetric urticarial lesions and a more generalized maculopapular eruption also can occur. Id reactions are most often associated with tinea pedis but also occur with tinea capitis.

Tinea Capitis

Clinical Manifestations

Tinea capitis is a dermatophyte infection of the scalp most often caused by Trichophyton tonsurans, occasionally by Microsporum canis, and, much less commonly, by other Microsporum and Trichophyton spp. It is particularly common in black children age 4-14 yr. In Microsporum and some Trichophyton infections, the spores are distributed in a sheath-like fashion around the hair shaft (ectothrix infection), whereas T. tonsurans produces an infection within the hair shaft (endothrix). Endothrix infections may continue past the anagen phase of hair growth into telogen and are more chronic than infections with ectothrix organisms that persist only during the anagen phase. T. tonsurans is an anthropophilic species acquired most often by contact with infected hairs and epithelial cells that are on such surfaces as theater seats, hats, and combs. Dermatophyte spores may also be airborne within the immediate environment, and high carriage rates have been demonstrated in noninfected schoolmates and household members. Microsporum canis is a zoophilic species that is acquired from cats and dogs.

The clinical presentation of tinea capitis varies with the infecting organism. Endothrix infections such as those caused by T. tonsurans create a pattern known as “black-dot ringworm,” characterized initially by many small circular patches of alopecia in which hairs are broken off close to the hair follicle (Fig. 658-3). Another clinical variant manifests as diffuse scaling, with minimal hair loss secondary. It strongly resembles seborrheic dermatitis, psoriasis, or atopic dermatitis (Fig. 658-4). T. tonsurans may also produce a chronic and more diffuse alopecia. Lymphadenopathy is common (Fig. 658-5). A severe inflammatory response produces elevated, boggy granulomatous masses (kerions), which are often studded with pustules (Fig. 658-6A). Fever, pain, and regional adenopathy are common, and permanent scarring and alopecia may result (Fig. 658-6B). The zoophilic organism M. canis or the geophilic organism Microsporum gypseum also may cause kerion formation. The pattern produced by Microsporum audouinii, the most common cause of tinea capitis in the 1940s and 1950s, is characterized initially by a small papule at the base of a hair follicle. The infection spreads peripherally, forming an erythematous and scaly circular plaque (ringworm) within which the infected hairs become brittle and broken. Numerous confluent patches of alopecia develop, and patients may complain of severe pruritus. M. audouinii infection is no longer common in the USA. Favus is a chronic form of tinea capitis that is rare in the USA and is caused by the fungus Trichophyton schoenleinii. Favus starts as yellowish red papules at the opening of hair follicles. The papules expand and coalesce to form cup-shaped, yellowish, crusted patches that fluoresce dull green under a Wood lamp.

Differential Diagnosis

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