Everyone knows someone with “hay fever.” Airborne pollens, molds, dust particles, etc. are inhaled and soon the sneezing and sniffling begins. A simple way to think of atopy for pets would be simply saying that the airborne allergen is inhaled by the pet but instead of sneezing and sniffling, the pet gets itchy skin. In fact, the situation is probably far more complex. The allergen is not only inhaled but is in contact with the skin and it is no longer considered accurate to think of atopy as an inhaled allergy. Exactly how we get from particles floating in the air, to itching and scratching is not entirely understood but the important issue is that the allergen comes from the air.
Airborne particles (pollens, danders etc.) are harmless to someone who is not allergic to them.
Allergy develops in individuals who are genetically programmed to do so.
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:
SeasonalityIn dogs, atopy usually produces a seasonal itchiness though after several years, the duration of the itchy period extends. Ultimately, the dog is itchy nearly all year round in 80% of cases. In cats, unfortunately, seasonality is not nearly as reliable a feature.
Young age of onsetSeasonal itchiness due to atopy tends to begin early in a pet's life (between ages 1 and 3 years in 70% of dogs diagnosed with atopy). Food allergy tends to begin later, more like age 5 or 6 years in dogs. Age at which itching first manifests is not as reliable a sign in cats as in dogs.
Good response to steroids. Whether the patient is a dog or cat, itchiness due to atopy responds rapidly to cortisone-type medications (prednisone, depomedrol, dexamethasone, etc.) as does itching due to insect bite allergy. Food allergy is more variable in its response; it may or may not respond well.
A positive intradermal skin test Intradermal skin testing is generally done in order to put together a set of allergens to make allergy shots. An area of non-inflammed skin is clipped of hair and small samples of different allergenic proteins are injected into the skin. An atopic patient should react to an allergen by showing swelling and redness in the area of injection. In most cases, this kind of testing is done after a diagnosis of atopy has been made based on other factors. This is not generally done to diagnose atopy but is done as part of the preparation for hyposensitization (see below). Sometimes, however, a diagnosis is elusive. In such cases, seeing a field of positive and negative skin blebs helps build confidence that atopy is the cause of the patients itching. There are blood tests that can also be helpful preparing for hyposensitization but it is important not to consider these tests as tests “for atopy.” They are instead tests of antibody levels and are used to help pick allergens for serum.
Typical irritation patternAtopy is associated with irritation in certain parts of the body. In the dog, these areas are: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: non-lesional fur mowing, eosinophilic granuloma complex, military dermatitis, face and ear itching.
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.
While it would be nice to have a blood test that could tell us if a pet’s itching is due to atopy, it is important to realize that such a test does not exist. Atopy remains a “clinical diagnosis” which means the diagnosis is made based on history and examination findings.
Before doing anything else, it is important to clear up secondary infections. Secondary infections involve bacteria (usually Staphylococcal) and/or yeast (Malassezia) at the site of the itchiest areas on the body. These organisms live naturally in the skin but when the skin is irritated, the gain access to inner tissue layers and proliferate. Sometimes they actually come to generate further allergic response in the skin. These infections tend to be recurrent and are the usual cause of recurrence of itch symptoms in a patient previously controlled.
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:
Excess urination (which could lead to house-breaking issues)
Suppression of the immune-system/bringing out latent infection (especially urinary tract infection and upper respiratory infection.)
Raising blood sugar/destabilizing a borderline diabetic (especially a problem for cats).In the short term, side effects can be controlled by adjusting dosage but in the long term, these medications are more problematic and if possible their use should be minimized.
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.
Reducing Allergen Exposure
The following are some general tips for minimizing allergen exposure:
Bathing the pet weekly to remove allergens from the fur may be helpful in reducing allergen exposure. There are also many therapeutic shampoos that can be used to restore the skin’s natural barrier or to assist in general itch relief.
Avoid stuffed toys, wash bedding regularly. This minimizes dust mite exposure. Also, remove the pet from the area when vacuuming or dusting.
Use air-conditioning and/or an air filter system.
Keep the pet away from the lawn while it is being mowed.
Just as people have allergy shots, so can pets; however, the process is not without difficulty and one should not expect hypo-sensitization to end all itchy skin concerns.
Allergy shots require approximately 6-12 months to begin working.
25% of atopic dogs will not respond (these are usually the animals allergic to multiple allergens.)
25% will require prednisone or similar steroid at least at some times.
You will most likely have to give the allergy shots yourself.
Referral to a veterinary dermatologist will likely be necessary.
In hypo-sensitization 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.”