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Use of Fungal Cultures in Diagnosing Tinea Capitis
Am Fam Physician. 2000 Apr 1;61(7):2192-2194.
Tinea capitis is a dermatologic condition that is frequently encountered in the pediatric population. Diagnosis is often difficult because children often present with nonspecific symptoms. The predominant organism, Trichophyton tonsurans, can produce a variety of scalp findings, ranging from mild pruritus to frank alopecia. In its later stages, tinea capitis is relatively easy to diagnose. However, it may also resemble seborrhea or folliculitis. A quick, confirmatory test is unavailable. Misdiagnosis will result in delay or improper treatment until the diagnosis can be confirmed by a fungal culture. Cultures can take several weeks to become positive, allowing T. tonsurans to spread to other children if treatment is withheld in the meantime. Hubbard conducted a study to determine the predictive value of clinical signs or symptoms in correctly diagnosing tinea capitis.
Children were enrolled in the study who presented to an outpatient pediatric clinic with at least one of four signs typically associated with tinea capitis (scaling of the scalp, scalp pruritus, diffuse, patchy or discrete alopecia, and adenopathy of the occipital or posterior auricular lymphatic chains) and were undergoing scalp culture. Children were excluded if they had been treated for tinea capitis within the previous year or if they presented with a kerion or pustular folliculitis. Scalp debris was collected from all children using the brush culture method and tested using the Dermatophyte Test Media (Acuderm, Inc.). A specific dermatophyte was identified for all positive cultures, and those without growth by day 28 were discarded.
A total of 47 boys and 53 girls was enrolled in the study. The average age was four years (range: seven months to 11 years). Of the four key clinical findings, scaling was noted in 93 percent, pruritus in 75 percent, alopecia in 73 percent and adenopathy in 65 percent of the participants. Cultures were positive in 68 percent of the children; T. tonsurans was the single isolated organism. The chance of having a positive culture correlated directly with the number of presenting signs and symptoms. All of the children with all four signs and symptoms had positive cultures. When three signs or symptoms were noted, 92 percent had positive cultures. Only 11 percent of cultures were positive if just two signs were present, and none of six children who presented with only one clinical finding had a positive fungal culture.
Cultures were positive for T. tonsurans in 55 children with adenopathy and alopecia (with or without scaling and pruritus). In contrast, when neither alopecia nor adenopathy was present, only one of 16 children had a positive fungal culture. Adenopathy and scaling were noted in 62 children, and all but two of these children had positive fungal cultures. Culture data are reviewed in the accompanying table.
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The author concludes that the presence of adenopathy, especially if accompanied by alopecia or scaling, is strongly predictive of a positive fungal culture in children in whom tinea capitis is suspected. If laboratory confirmation is unavailable or may be delayed, empiric treatment of children with these clinical findings is appropriate.
Hubbard TW. The predictive value of symptoms in diagnosing childhood tinea capitis. Arch Pediatr Adolesc Med. November 1999;153:1150–3.
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