Common mistakes in dermatitis case workups - DVM
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Common mistakes in dermatitis case workups


DVM InFocus


Use the proper technique when performing skin scrapes. Occasionally, the harried practitioner uses a therapeutic trial to determine whether demodicosis is contributing to chronic skin disease. But Demodex is not an invisible parasite. If it is contributing to skin disease, it can usually be found with the proper skin scraping technique, which includes:

  • Properly restrain the patient.
  • Choose at least three good sites to scrape—lesions, preferably those with papules, patchy alopecia, or patches of comedones.
  • Clip the sites to be scraped using a #40 blade.
  • Pinch the skin at the site to extrude follicular contents.
  • Scrape deep enough with a dull surgical blade or a spatula to produce capillary bleeding.

The latter two steps are somewhat painful and should not, in my opinion, be done in the presence of the client.

Perform DTM cultures. In cats, ringworm has many potential clinical presentations. In my opinion, virtually every feline dermatology patient should have a DTM culture of a properly obtained sample. The barriers that frequently block a DTM culture from happening are:

  • Expense. The culture adds extra expense to a routine dermatologic workup so the practitioner must be prepared to explain why the possibility of ringworm should be eliminated early in the course of working up a skin problem.
  • Technique. Some veterinarians are not comfortable with obtaining the right specimen for the best outcome in DTM culture. The bottom line is maximizing the amount of potentially infected material obtained and minimizing material that is potentially contaminated with saprophytic fungi from the environment.

CLIP OR SCISSOR—TO ABOUT ONE-QUARTER INCH—THE LESION AND SURROUNDING AREA. GENTLY PAT THE AREA WITH A BARELY MOISTENED ALCOHOL SPONGE. THIS FURTHER REMOVES CONTAMINATION.

PLUCK AND SCRAPE A LIBERAL SAMPLE OF HAIR AND SCALE FOR THE CULTURE.

  • Interpreting the DTM results. This is an area that can cause much frustration. In some cases, the practice may want to send their inoculated media to a microbiology laboratory. If the DTM is to be incubated and evaluated in the hospital, the sample should be stored at around 78F (25C) and evaluated daily for the diagnostic color change. Someone in the clinic should be prepared to follow through with positive samples in seven to 10 days to make a microscopic identification of the suspect colonies as well.
When presented with a complicated dermatology case, remember to have a system, look for the underlying primary process, and keep allergies on your differential diagnosis list.


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Source: DVM InFocus,
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