Allergy specific immunotherapy: how to maximize the results (Proceedings)
Allergen specific immunotherapy (desensitization or "allergy shots") has been one of the mainstays of care in specialized dermatology practice for years. In the mid 1980s serology (RAST) testing was marketed to veterinarians, and since then numerous companies have developed their own RAST or ELISA tests. Intradermal allergy testing (skin testing) is the traditional test performed by most veterinary dermatologist. The number, purity, and specificity of extracts available for skin testing and immunotherapy have improved over the years. The diagnosis of atopy should be made based on history, clinical presentation and the ruling out of other hypersensitivities such as parasite and food allergy and not based on any type of allergy test.
Allergen specific immunotherapy is most definitely not a "one size fits all" program. If a veterinarian wants to become proficient at administering immunotherapy, she or he should first become familiar with the regional pollen producing plants, when they bloom, how long they bloom, and how prevalent the plant (and allergen) is in the area. An awareness of the prevalence of indoor, potentially year round allergens, such as house and storage mites, mold spores, animal and human dander and insect particles is also necessary. This knowledge will enable the veterinarian to more effectively determine or prioritize what each individual patient should be desensitized to. The first critical step in achieving success with immunotherapy is determining accurately and completely what the patient is allergic to. In our practice we utilize intradermal skin testing almost exclusively for defining what an atopic patient is allergic to. We find we get the most specific and sensitive results from intradermal testing. This also allows us to customize the list for which we are testing based on specific location, not just region. Does it really make sense to lump Southern Arizona in the same region as northern Montana when considering what allergens to test for? Intradermal allergy testing is expensive to set up and maintain, and requires practice and skill interpreting results and is therefore mostly performed only in a specialty setting. If intradermal testing is not available, then serology testing must be utilized.
It should be emphasized that the only reason to perform any type of allergy (blood or skin) testing is to follow-up with immunotherapy. Once allergy test results are obtained, these results should always be critically analyzed to insure that the results are consistent with the patients' pruritus history. This determination will include historical information regarding seasonality. If allergy testing reveals positive reactions only to seasonal pollens in a patient which is pruritic year-round, then something is being missed! Choosing the allergens to be included in the extract is something the veterinarian should personally direct based on the specifics of each individual patient. This is where knowledge of the regional allergens is necessary. For the outdoor working dog that is pruritic only in the summer and fall, then positive reactions to grasses and weeds should be present, and they need to be emphasized or prioritized when formulating the extract. For the indoor Chihuahua which sleeps under the covers at night and who is pruritic year round, then indoor allergens such as dander, mold spores, house dust and house mites need a higher priority in the extract recipe. Yet another factor to consider when developing the "correct" mix or recipe is how long particular pollen is present. In our practice Bermuda grass is one of the dominant pollens, and Bermuda will bloom for over six months in our area. Most tree pollens are present for 2-6 weeks. Does it make sense to put equal levels of a tree pollen and Bermuda grass? Or equal levels of house mites and Ash tree pollen in the patient pruritic year round? One should not assume that the allergens in a vial all have to be equal quantity or volume. If Oak is a significant reaction in a dog on the central California who is the most pruritic in spring, why not double (or more) the quantity of Oak pollen compared to some of the other ingredients. Our current skin test panel includes 70 different allergens. A number of our patients will have significantly strong skin test reactions to over twenty different positive allergens and some will have over 50 significantly positive reactions. In such cases we will often utilize two different vials of allergen to more fully incorporate all the positives into the immunotherapy program. Another reason to utilize two different vials of allergens is when significant reactions to mold spores occur. Some molds may have proteolytic enzymes which have the potential to degrade pollen proteins when mixed in the same vial. In such cases, placing the molds in a second, separate vial can alleviate this concern.