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COPYRIGHT 2008 American Academy of Family Physicians
The common dermatophyte genera Trichophyton, Microsporum, and Epidermophyton are major causes of superficial fungal infections in children. These infections (e.g., tinea corporis, pedis, cruris, and unguium) are typically acquired directly from contact with infected humans or animals or indirectly from exposure to contaminated soil or fomites. A diagnosis usually can be made with a focused history, physical examination, and potassium hydroxide microscopy. Occasionally, Wood's lamp examination, fungal culture, or histologic tissue examination is required. Most tinea infections can be managed with topical therapies; oral treatment is reserved for tinea capitis, severe tinea pedis, and tinea unguium. Topical therapy with fungicidal allylamines may have slightly higher cure rates and shorter treatment courses than with fungistatic azoles. Although oral griseofulvin has been the standard treatment for tinea capitis, newer oral antifungal agents such as terbinafine, itraconazole, and fluconazole are effective, safe, and have shorter treatment courses.
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Tinea refers to dermatophyte infections, which are generally classified by anatomic location: tinea capitis is located on the scalp, tinea pedis on the feet, tinea corporis on the body, tinea cruris on the groin, and tinea unguium on the nails. Tinea is also called ringworm, especially when located on the body, and is caused by a group of fungi that infect only the outer keratinous layer of skin, hair, and nails. These fungi cannot survive on mucosal surfaces, such as the mouth or vaginal area. Superficial tinea infections are some of the most common dermatologic conditions in children. (1)
Dermatophytes are aerobic fungi that are divided into three genera (i.e., Trichophyton, Microsporum, and Epidermophyton). Tinea infection is acquired directly from contact with infected humans (anthropophilic organisms) or animals (zoophilic organisms) or indirectly from exposure to contaminated soil or fomites (geophilic organisms). The clinical manifestations of dermatophyte infections varies by the infection site and the patient's immunologic response; genetic susceptibility may play a role in vulnerability to infection. (2)
Table 1 presents the differential diagnosis of tinea infections, (3) and Table 2 summarizes common therapies.
Diagnostic Tests
MICROSCOPY
Potassium hydroxide (KOH) microscopy is essential for the office-based diagnosis of tinea infections. (1,2,4,5) This technique directly shows hyphae and confirms infection. The specimen is examined under the microscope after a drop of 10 to 20 percent KOH solution is added to the scraping from the active border of the lesion. KOH microscopy has good sensitivity and is more sensitive than a fungal culture. A positive test result justifies initiation of treatment. KOH microscopy has a 76.5 percent sensitivity and an 81.6 percent negative predictive value for the diagnosis of tinea unguium compared with a 53.2 percent sensitivity and 69.0 percent negative predictive value with culture. (4)
CULTURE
Culture techniques have a limited role in the evaluation and treatment of suspected tinea infection because of the expense and time requirement. However, when the need for long-term oral therapy is anticipated, the infection seems resistant to standard topical therapy, or the diagnosis is unclear, a culture is an appropriate approach for laboratory confirmation.
WOOD'S LAMP EXAMINATION
Wood's lamp examination for the diagnosis of tinea infection has decreased to near disuse because of the gradually declining number of dermatophytes that fluoresce under ultraviolet light. (2,5) Exceptions include tinea capitis caused by zoophilic Microsporum canis and Microsporum audouinii, which fluoresce blue-green; tinea (pityriasis) versicolor caused by Malassezia furfur, which fluoresces pale yellow to white;...
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