Canine atopy can be hard to distinguish from sarcoptic mange (scabies), demodectic mange (demodicosis), flea bite allergies, food allergies and other skin disorders, which makes it somewhat difficult to diagnose. When a dog arrives at a veterinary clinic with a history of itching, scratching, licking, rubbing and biting at its skin, the veterinarian will gather detailed information from the owner about the dog’s health and background. This may include: 1) when the symptoms started, 2) whether they come and go or have stayed about the same, 3) what the dog eats and whether there have been any recent changes in its diet, 4) whether the dog is on any flea, tick or heartworm preventatives, and 5) whether any other animals in the household are showing similar signs.
The doctor will conduct a thorough physical examination, looking closely at the dog’s skin and coat for evidence of external parasites and areas of hair loss. Sometimes, the dog’s history and physical examination results will point to a presumptive diagnosis of atopy. Before a definitive diagnosis of atopy can be made, other causes of the dog’s symptoms must be ruled out.
How Atopy is Diagnosed
A number of diagnostic techniques are available to help the veterinarian rule out other potential causes of the dog’s condition. Deep skin scrapings can be evaluated under a microscope to check for Demodex mites. Plucked hairs can also be looked at microscopically for evidence of abnormalities (trichography). Swabs taken from rashes and sores can be sent to a laboratory for bacterial and fungal analysis and culture. Tissue samples can be collected by fine needle aspiration or biopsy. If food allergies are suspected, the veterinarian may recommend an elimination diet trial.
Intradermal skin testing, similar to that performed on people, is the “gold standard” for diagnosing environmental hypersensitivities such as atopy. Usually, it only is performed after any drug therapy has been stopped long enough for all of the pharmaceutical agents to be eliminated from the dog’s system. Depending on the drug, this can take weeks to months. Once that time has passed, the veterinarian will inject tiny amounts of substances, known to cause canine skin allergies, into specific areas under the dog’s skin. After waiting a prescribed period of time, she will evaluate the injection sites for any adverse reactions which, if present, indicate that the dog is allergic to those injected substances. This process can be time consuming and costly, and it is not offered at most general veterinary practices.
If intradermal testing is unavailable or impractical, serum tests can be used to detect antibodies to certain allergens in the dog’s blood. These tests are less expensive, less risky, less painful and more convenient than intradermal allergy tests. Their results are also less reliable.
Canine atopy is one of the most frustrating skin disorders faced by owners, veterinarians and dogs. However, with time, dedication and patience, the symptoms of atopy usually can be managed successfully.