Biopsy is not necessary except in deep mycosis. Superficial types show hyperkeratosis and keratinous follicular plugs. PAS or Gomori-Grocott stains show filaments in the horny layer. Neutrophils, vasodilatation and a mild to dense lymphohistiocytic infiltrate are seen. In kerion there are pustules or abscesses, and spores and/or filaments can be found in the dermis. In the trichophytic granuloma, besides the presence of the parasite, giant and epithelioid cells are observed.
A Wood's lamp is useful in the microsporic tinea capitis. There is a green fluorescence. Direct examination with KOH plus dimethylsulfoxide or with black chlorazol shows filaments and spores. In trichophytic tinea capitis, hair reveals endothrix spores (trichophytic and favic type) and on microscopy, ectoendothrix spores (microsporic, microide and megasporic types), which indicates filaments and spores are found inside and/or outside the affected hair. An easy way to collect the parasitized hair is to rub the affected hairy skin area with saline-soaked gauze. Culture can be done with a sterile swab, a piece of floor carpet or with a tooth
brush. Culture on Sabouraud's medium with or without antibiotics allows growth (1-2 weeks, or more) and identification of the causal agent. The trichophytin test is not of practical use.
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