How is tinea cruris (jock itch) diagnosed?

Updated: Feb 22, 2018
  • Author: Michael Wiederkehr, MD; Chief Editor: Dirk M Elston, MD  more...
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Microscopic examination of a potassium hydroxide (KOH) wet mount of scales is diagnostic in tinea cruris. The procedure for KOH wet mount is as follows:

  • Clean the area with 70% alcohol.

  • Collect scales from the margin of the lesion; use a scalpel or the edge of a glass slide for this purpose. Cover the collected scales with a cover slip; allow a drop of KOH (10-15% wt/vol) to run under the cover slip.

  • The keratin and debris should dissolve after a few minutes. The process can be hastened by heating the slide or by the addition of a keratolytic or dimethyl sulfoxide to the KOH formulation.

  • The addition of 1 drop of lactophenol cotton blue solution to the wet mount preparation heightens the contrast and aids in the diagnosis.

  • Negative results on KOH preparation do not exclude fungal infection.

  • Scale culture is useful for fungal identification but is a more specific, albeit less sensitive, diagnostic test than KOH wet mount.

Growth on Mycosel or Sabouraud agar plates usually is sufficient within 3-6 weeks to allow specific fungal identification.

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