AIRBORNE ALLERGIES (ATOPIC DERMATITIS)
Airborne particles (pollens, danders etc.) are harmless to someone who is not allergic to them.
Breeds predisposed to develop atopy
FEATURES OF ATOPY
There are many reasons for pets to itch: parasites, allergy to flea bites, food allergy, secondary infection and the list goes on. The following are findings in the history and examination of the patient that might lead to a diagnosis of atopy:
A few reactive blebs on an intradermal skin test
(original graphic by marvistavet.com)
It should be noted that food allergy presents with a very similar irritation pattern but a different history. Flea bite allergy, the most common form of allergic skin disease in pets, has a different irritation pattern.
In cats, the irritation pattern is not as characteristic. There are four common manifestations of atopy:
Unfortunately, these same irritation patterns can be found in numerous other skin conditions and, in fact, up to 25% of atopic cats have multiple types of allergies.
Making the Skin Less Reactive
Since it is unlikely that the patient is going to be able to avoid airborne allergens (pollens, for example, travel miles in the breeze), we are left with treating the patient. For short episodes of itching during the itchy season, cortisone-type medications are highly effective. When the pet becomes more chronically itchy, cortisones become less feasible because of their long term side effects and other options must be considered.
These cortisone-type medications (prednisone, prednisolone, triamcinolone, dexamethasone etc.) tend to be useful as the "first line of defense" against itchy skin. A higher dose is used at first but this is quickly tapered down once the condition is controlled. Prednisone, for example, is given every other day so as to allow the pet one day of recovery from the prednisone's hormonal actions. An atopic dog will respond within days. For cats, long-acting cortisone-type injections are commonly used as cats are frequently not amenable to taking pills.
Side effects include:
OMEGA 3 FATTY ACID SUPPLEMENTS
These products are NOT analogous to adding oil to the pet's food. Instead, these special fatty acids act as medications, disrupting the production of inflammatory chemicals within the skin. By using these supplements, it may be possible to postpone the need for steroids/cortisones or reduce the dose of steroid needed to control symptoms. It takes a good 6 weeks to build up enough omega 3 fatty acids in the body to see a difference.
These are far less harmful than prednisone but only 10-20% of dogs will respond to any given antihistamine. Fortunately, there are numerous antihistamines to try and often it is possible to find one that works by trying a different one sequentially. In contrast to the dog, cats are far more responsive to antihistamines, the downside being having to give a cat medication twice daily. Antihistamines and omega 3 fatty acids synergize with each other so it is a good idea to use omega 3 fatty acids in conjunction with antihistamines.
Cyclosporine is a modulator of the immune response that has been very helpful in organ transplant patients both human and non-human. It has been found to be as reliably effective in atopic dermatitis in the dog as steroids and does not carry the unpleasant side effect profile that steroids do. It is used mostly in dogs but can also be used in cats. For more details on this medication click here.
This is a new drug still under development. It addresses mast cells, the cells that carry the inflammatory biochemicals of allergy. It is currently available on a very limited basis through its manufacturer as part of clinical research.
Reducing Allergin Exposure
The following are some general tips for minimizing allergen exposure:
Just as people have allergy shots, so can pets; however, the process is not without difficulty and one should not expect hyposensitization to end all itchy skin concerns.
In hyposensitization the patient is injected with small amounts of allergens on a regular basis. As time passes, the amounts of allergens increase and injections are given at longer intervals. The selection of allergens is made based on the results of either an intradermal skin test (as described above), an “in vitro” test (a blood test) or a combination of the results of both tests.
IS YOUR PET A CANDIDATE FOR SKIN TESTING?
Testing is best done during your pet's non-itchy season (if there is one) so that the skin responses of the test will not be clouded by active inflammation. The test involves injections of small amounts of allergen extracts into the skin. Reactions noted are compared to reactions produced by two controls: pure histamine (very inflammatory) and pure saline (very non-inflammatory).
In order for skin testing to be performed, medications must be discontinued well in advance. How long in advance depends on the medication and on the policies of the veterinary dermatology practice that will be doing the test. Oral steroids, for example, commonly require a full month discontinuance, which can be problematic if the pet is highly dependent on medication for life quality.
IN VITRO TESTING?
In vitro testing does not always require withdrawal of medications nor does it require referral to a specialist. There is no hair clipping and sedation is rarely necessary. Blood is simply drawn and checked for antibodies against common allergens for that geographic region. A profile is reported and allergens can be selected accordingly. It is important to remember that these results do not necessarily imply that the patient is allergic to substances reported; this is simply a test for antibodies. Antibody elevations are very common with levels changing based on an assortment of factors (whether the pet has parasites at the time of the test, how common the substances being tested are, how long medications have been used prior to the test etc.) and interpretation of the profile is part of the “art of veterinary practice.”
For more details on what is involved, see our page on Allergen-Specific Immunotherapy (Allergy shots).
To find a veterinary dermatologist in your area, visit the web site of the American College of Veterinary Dermatology at www.acvd.org.
Page last updated: 1/1/2012