Individuals of both sexes and all age groups are affected by dermatophytes; however, children under the age of 10 rarely present with tinea pedis. The main clinical pictures are those of localised tinea pedis, interdigital, plantar hyperkeratotic, and onychomycosis. Common names for these conditions include ringworm and athlete's foot. Dermatophyte infections can manifest as localised single or multiple circinate plaques with erythema and variable degrees of scaling on the body in cases of tinea corporis (Figure 9.17). Athlete's foot involves the dorsum or per-
malleolar regions. Toe-web involvement is commonly bilateral, presenting with erythema, a burning sensation, pruritus and scaling, particularly of the fourth interdigital toe web space. Severe acute forms present with painful erythema and blistering in a similar pattern to that found in cases of acute eczema or pompholix. Patients with a history of atopy are predisposed to superficial infections by dermatophytes, and in these cases erythematous inflammatory fungal lesions coexist with patches of ecze-matous skin (Figure 9.18). Chronic plantar lesions develop asymptomatic large hyperkeratotic plaques and a particular form of toenail infection by T.rubrum manifests clinically as a subungual white onychomycosis. Varying degrees of temporary disability may result from severe infections. Children manifest scalp infections under the kerion clinical form with patches of nonscarring alopecia and boggy inflammation of the skin (Figure 9.19). Less commonly, adult travellers manifest granulomatous inflammation with varying degrees of scarring in infections caused by other species of Trychophyton (Figure 9.20).
Discrete plaques of granuloma annulare have to be considered in the differential diagnosis of localised ringworm, whereas thickenned plaques of plantar psoriasis
may pose diagnostic difficulties with chronic hyper-keratotic infections by dermatophytes. Other superficial skin and nail infections of the foot, such as those caused by Candida and Scytalidium species, may also present a diagnostic difficulty. The returning traveller from the tropics is often referred to our specialised clinic with severe or recurrent superficial yeast infections by Malas-sezia furfur (Figure 9.21).
The diagnosis of dermatophyte infection on the skin is made on clinical grounds. Additional diagnostic measures include direct microscopy of skin scrapings in 10-12% KOH solution, and the identification of the causative organism by culture in Sabouraud medium. A similar strategy is recommended for the laboratory diagnosis of pityriasis versicolor (malasseziosis), which requires special oily additives for successful isolation in culture.
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