Ringworm on Scalp (cont.)
Exams and Tests
- When the scalp is examined with a Wood lamp that transmits ultraviolet light, the base of the hair shaft will light up a blue-green fluorescent band if Microsporum species is present. This is due to deposits of metabolic byproducts that this species leaves. Because this species is no longer common in the United States, this technique is less useful and not routinely performed.
- More commonly, the doctor can diagnose scalp ringworm with a visual inspection and by observing the symptoms present. However, scrapings examined in the laboratory are sometimes needed to confirm the diagnosis and may be helpful if repeated to make sure the ringworm is treated.
- The following are methods of collecting tissue samples for microscopy:
- Scraping the scalp with a surgical blade and removing the hair with a needle and forceps
- Running a toothbrush over the scalp about 10 times to collect the scales and hair (this is the best method)
- Cotton swabs
- Moistened gauze
- Once tissues have been collected, a 10%-15% solution
of KOH (potassium hydroxide) is added and the slide is studied under a microscope to look for fungal spores. This method is fast, but it is effective in finding present fungal spores only 50% of the time.
- The best method of diagnosis is culture. The collected specimen is placed in a medium that provides fungal food to see if growth takes place. This method naturally takes more time, and an answer takes
seven to 10 days.
Lisandro Irizarry, MD, MPH, FAAEM
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