When is Wood lamp exam indicated in the workup of tinea capitis (scalp ringworm)?

Updated: Feb 21, 2020
  • Author: Marc Zachary Handler, MD; Chief Editor: Dirk M Elston, MD  more...
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Answer

When a diagnosis of ringworm is under consideration, the scalp is examined under a Wood lamp. If fluorescent infected hairs are present, hairs are removed for light microscopic examination and culture. Infections caused by Microsporum species fluoresce a typical green color.

Unfortunately, most tinea capitis infections in North America are caused by T tonsurans and do not demonstrate fluorescence. [24]

In favus, infected hairs appear yellow (see the image below).

Wood lamp examination of a gray-patch area on the Wood lamp examination of a gray-patch area on the scalp. In Microsporum canis infection, scalp hairs emit a diagnostic brilliant green fluorescence. Trichophyton tonsurans does not fluoresce with Wood lamp.

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