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INTRODUCTION TO CHAPTER

A few simple diagnostic skin procedures such as potassium hydroxide (KOH) examinations, Tzanck smears, and scrapings for scabies can be valuable tests to confirm a clinical diagnosis. However, these tests can have false-positive and false-negative results which are typically due to the following problems:

  • Improper site or lesion selection

  • Faulty collection technique

  • Failure to systematically scan entire specimen

  • Artifacts in the specimen

Polymerase chain reaction (PCR) tests are replacing some of the diagnostic tests used in dermatology, but they are more expensive and are not yet widely available in all clinical settings.1–3

KOH EXAMINATIONS AND FUNGAL CULTURES

KOH examinations (Table 4-1) are a cost-effective method for the detection of superficial fungal skin infections. In the hands of an experienced clinician this test has a high level of specificity and sensitivity. However, cotton or nylon fibers from clothing and socks can mimic fungal hyphae, a mosaic artifact created by cell walls can also mimic fungal hyphae, and air bubbles can mimic spores. Some of these false positives can be reduced by the use of special stains such as Chicago Sky Blue4 or Chlorazol Black E. Fungal cultures are another option for detection of fungal infections. Dermatophyte Test Media (DTM), a modified Sabouraud agar contains an indicator dye that turns red within 7 to 14 days in the presence of viable dermatophytes (Figure 4-3).

Table 4-1.Potassium hydroxide (KOH) examination for superficial fungal infections.

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