Tinea Faciei Workup

Updated: May 20, 2019
  • Author: Robert A Schwartz, MD, MPH; Chief Editor: Dirk M Elston, MD  more...
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Workup

Laboratory Studies

Even in the best mycology laboratories, as many as 30% of culture results may be negative, particularly in chronic infections.

Mycologic investigation is essential in the diagnosis of tinea faciei. It includes direct microscopic examination for hyphal elements and culturing.

The collection of the surface scrapings is important for laboratory studies. The material should be obtained from the border of the lesions where the more severe inflammatory reaction occurs and where more fungal elements are present.

Direct microscopic examination is the easiest mycologic procedure. Scrapings are placed in 10-20% potassium hydroxide (KOH) solution, usually with the addition of dimethyl sulfoxide (DMSO). The latter helps to dissolve background keratinocytes to enable visualization of the fungal elements. After warming the slide for a short time, the specimen is examined with a light microscope. Some authors suggest detection is enhanced with special stains, such as chlorazol black E, Parker blue-black ink, or Swartz-Lamkin stain.

Culturing allows the identification of the causative pathogen. Culturing is performed routinely with Sabouraud agar and the addition of cycloheximide and chloramphenicol. These substances inhibit the growth of bacteria and other contaminants. After 3-4 weeks of incubation, the final identification is based on morphologic and microscopic findings in the colonies.

Dermatophytes may be diagnosed by using special media for rapid detection. This media contains a color indicator that changes from yellow to red with the growth of dermatophytes after a few days of incubation.

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Histologic Findings

Histologic examination may occasionally be useful for establishing the diagnosis, but it is usually unnecessary. Its pattern is variable, ranging from mild focal spongiosis to a chronic spongiotic psoriasiform dermatitis with a mixed dermal inflammatory infiltrate and fungi in the cornified layer. [21] Routine histopathologic evaluation with hematoxylin-eosin staining may reveal cutaneous fungal elements, but periodic acid–Schiff (PAS) staining is recommended to facilitate visualization.

Hyphae may be detected in the stratum corneum of the epidermis. Infections with T rubrum or Trichophyton verrucosum may invade hairs and follicles. A mixed cellular inflammatory infiltrate is usually present in the papillary dermis, and neutrophils may extend into the horny layers above.

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