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  • • Suspected fungal or candidal infection.

  • • Glass microscope slide and coverslip.

    • 10–20% potassium hydroxide (KOH).

    • Microscope.

    • #15 scalpel blade or other device to scrape skin (edge of microscope slide, cytobrush, or foman blade).

    • Matches.

  • • Minimal discomfort and bleeding with aggressive scraping.

  • • This technique is most commonly used in diagnosing tinea corporis or tinea pedis.

    • Although a lower sensitivity is found with this diagnostic test for tinea capitis, spores within hair shafts can be visualized in “black dot” type.

    • Samples should be collected from the advancing edge or margins of skin lesions with the edge of a scalpel.

    • • In children, use the dull edge if they are moving or use a cytobrush.

      • The foman blade, a 2-sided, spatula-type instrument, is less likely to cut the skin of a moving infant.

    • Shavings of nails left in KOH for several hours may assist in diagnosis of onychomycosis.

    • KOH is used to digest the proteins, lipids, and epithelial debris in the specimen.

    • Gentle cleaning of the area to be tested with an alcohol wipe before this examination may remove confusing oil drops and excess debris from the slide.

  • • Parents and patients should be aware that scraping may cause minimal bleeding and mild discomfort.

  • • Patient should be positioned in good lighting with access to lesion to be tested.

  • • Obtain a skin or nail specimen with gentle scraping of the areas to be tested.

    • Place scale, roof of vesicle, or nail shavings on a glass slide.

    • Scrape with the edge of the #15 blade, the edge of a glass microscope slide, or a foman blade.

    • Apply 1–2 drops of KOH over the specimen.

    • Place a coverslip over specimen and press firmly.

    • Consider gentle heating of the underside of the slide for 5–10 seconds until the epithelial cells and debris dissipate.

  • • The hyphae can be seen under low power (Figure 40–1), but better observation of both hyphae and spores is obtained by use of a dry high objective with reduced illumination.

  • • The juncture lines of epithelial cells may be mistaken for hyphae. Cell walls have irregular linearity.

    • Positive preparations appear as septate and branching hyphae. A positive KOH preparation should reveal definite hyphae traversing epidermal cells.

    • Fabric fibers (usually twisted and uniform) and hairs are larger than hyphae.

    • If a tinea or candidal infection is strongly suspected and this examination is negative, consider performing a culture.

Figure 40–1.

Hyphae under microscope.

  • • This is a diagnostic examination that is underutilized due to lack of experience with interpretation. The identification of spores and hyphae becomes more straightforward the more often the test is done.

  • • As indicated after appropriate treatment.

Cunningham ...

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