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INTRODUCTION TO CHAPTER

This chapter covers selected diagnostic tools that a clinician can use in the office to confirm their diagnoses including laboratory tests, patch testing, and dermoscopy.

A few simple diagnostic tests such as potassium hydroxide (KOH) examinations, Tzanck smears, and scrapings for scabies can be helpful to confirm a clinical diagnosis. However, these tests can have false positive and false negative results which are typically due to the following problems most of which are operator dependant.1

  • Improper site or lesion selection

  • Faulty collection technique

  • Failure to systematically scan entire specimen

  • Artifacts in the specimen

Polymerase chain reaction (PCR) tests for herpes and fungal infections are replacing some of the diagnostic tests used in dermatology, but they are not yet widely available in all clinical settings.2,3

The use of a dermatoscope to visualize structures that are beneath the surface of the skin has become a major diagnostic tool in dermatology. This chapter will focus on dermoscopy of skin tumors. However, dermoscopy is useful in the diagnosis of many other disorders such as hair diseases and dermatoses.4

POTASSIUM HYDROXIDE (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 and a mosaic artifact created by cell membranes 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 Blue or Chlorazol Black E.5 Fungal cultures are another option for detection of fungal infections. Dermatophyte Test Media (DTM) media, a modified Sabouraud's agar contains an indicator dye that turns red within 7–14 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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