Athlete's foot laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Sanjana Nethagani, M.B.B.S.[2]

Overview

  • Athlete's foot can usually be diagnosed by visual inspection of the skin, but where the diagnosis is in doubt direct microscopy of a potassium hydroxide preparation (known as a KOH test).[1]
  • A KOH preparation is performed on skin scrapings from the affected area.
  • The KOH preparation has an excellent positive predictive value, but occasionally false negative results may be obtained, especially if treatment with an anti-fungal medication has already begun.

Laboratory Findings

Microscopy

  • Skin scrapings from affected areas of toes, web spaces, soles including scales can be taken.[2]
  • To diagnose vesicular tinea pedis, the entire roof of the bulla is removed and mounted for a high yield of fungus.
  • Scrapings are stained with KOH and viewed under a microscope.
  • Counterstains may be used to better visualize the fungus such as chorazol black which is specific for chitin.
  • Dimethyl sulfoxide may be used to dissolve keratin in the scrapings.

Biopsy

  • A biopsy of the affected skin (i.e. a sample of the living skin tissue) can be taken for histological examination.

Culture

Immunochromatography

  • Immunochromatography kits use a solution to extract dermatophyte antigens from a tissue sample and detect their reaction with monoclonal antibodies to these antigens.[4]
  • This method is effective for tinea unguium but not very effective for tinea pedis.
  • Samples that test positive with this method are re-examined using microscopy or culture methods to make a final diagnosis.

References

  1. del Palacio, Amalia. "Trends in the treatment of dermatophytosis" (PDF). Biology of Dermatophytes and other Keratinophilic Fungi: 148–158. Retrieved 2007-10-10. Unknown parameter |coauthors= ignored (help)
  2. Nenoff P, Krüger C, Schaller J, Ginter-Hanselmayer G, Schulte-Beerbühl R, Tietz HJ (2014). "Mycology - an update part 2: dermatomycoses: clinical picture and diagnostics". J Dtsch Dermatol Ges. 12 (9): 749–77. doi:10.1111/ddg.12420. PMID 25176455.
  3. Gupta AK, Chaudhry M, Elewski B (2003). "Tinea corporis, tinea cruris, tinea nigra, and piedra". Dermatol Clin. 21 (3): 395–400, v. doi:10.1016/s0733-8635(03)00031-7. PMID 12956194.
  4. Tsunemi Y (2017). "Dermatophyte Antigen Kit". Med Mycol J. 58 (2): J51–J54. doi:10.3314/mmj.17.005. PMID 28566667.

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