Tinea Pedis Workup
- Author: Courtney M Robbins, MD; Chief Editor: Dirk M Elston, MD more...
In suspected tinea pedis, order direct potassium hydroxide (KOH) staining for fungal elements. Usually, the fungal elements are easily identified from scaly lesions. Using counterstains may enhance the visibility of the hyaline hyphae found in dermatophyte infections. Examples include the chitin-specific stains chlorazol black E, which stains hyphae blue-black, and calcofluor, which fluoresces hyphae under a fluorescent microscope.
A sample from skin scrapings may be obtained using a No. 15 blade. When blisters are present, the highest fungal yield is obtained by scraping the roof of the vesicle.
A fungal culture may be performed to confirm the diagnosis of tinea pedis and to identify the pathogenic species. Common media include dermatophyte test medium, Mycosel, or mycobiotic agar. Use caution when choosing the correct culture medium because certain media (eg, dermatophyte test medium) contain cycloheximide, which inhibits the growth of nondermatophyte molds. Because these fungi can be a factor in tinea pedis, use agar without cycloheximide.
A skin biopsy and histopathological study are rarely needed to confirm a diagnosis of tinea pedis. Fungal elements within the stratum corneum can usually be identified using periodic acid-Schiff or Gomori methenamine-silver stain but may be sparse or absent in inflammatory or interdigital tinea pedis complicated by secondary bacterial infection. Neutrophils may be noted within the stratum corneum, a finding that should prompt consideration of a dermatophyte infection. In vesicular tinea pedis, spongiotic intraepidermal vesicles are present; in the chronic hyperkeratotic (moccasin) type, hyperkeratosis and epidermal acanthosis usually are present. Both types are associated with an acute or chronic dermatitis that may contain eosinophils.
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