Section: Veterinary Care In-depth
Diagnosis In-depth
A thorough history and physical exam are imperative to making an appropriate diagnosis. The distribution of skin lesions will often allow the clinician to limit the list of differential diagnoses. Some commonly performed tests include:
Skin scrapes- A surgical blade is used to gently scrape the skin surface to look for various types of mites or mite eggs.
Skin cytology- Smears of fluid or pus filled vesicles or inflamed skin are helpful to diagnose bacterial and yeast infections.
Complete blood count and biochemical profile- These tests are not necessary in every case of dermatitis. They evaluate the blood cells and organ function, and may be useful if an underlying systemic disease is suspected. These tests are especially useful if the patient has other signs of illness in addition to the dermatitis.
Allergy blood tests- These are special tests designed to find out which allergens the animal is responding to. Although they can be useful, the test results are not always reliable.
Intradermal allergy testing- This involves testing the skin for allergic responses by injecting small amounts of known allergens into pre-determined locations in the skin. This type of testing is generally more reliable than the blood tests, but interpretation can be difficult and false test results may occur if not performed properly. Only a trained dermatologist, or a doctor who does many intradermal allergy tests and is familiar with the test interpretation should perform these. Allergy testing of this sort is usually done in cases of suspected atopy.
Dietary trials- If an animal is suspected of having a food allergy, special dietary trials are the best way to make the diagnosis. This entails putting the pet on an elimination diet, consisting of a protein source that the animal has not previously eaten. Home-cooked diets or prescription diets can be fed. In order for the trial to be successful, all other foods must be excluded. This includes treats, rawhides, flavored vitamins or flavored heartworm medications, and table food. It may take a number of weeks on the diet before the animal shows any improvement in the dermatitis.
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