UNDERSTANDING ITCHY PETS AND ALLERGIES
What is skin allergy?
Skin allergy in pets includes several specific conditions which include: inhalant allergic dermatitis (also known as atopy), contact allergic dermatitis, fleabite hypersensitivity, and bacterial (staphylococcal) hypersensitivity, and food allergy. These conditions differ by which substances cause the allergy, and how the allergens enter the body. The reaction in the skin of the animal is similar regardless of the specific type of allergy.
The response of the skin to the allergen is inflammation. With inflammation four symptoms occur: redness, heat, swelling, and pruritis (itchiness). The owner usually notices the animal's response to inflammation, which includes persistent scratching, chewing, or rubbing of the skin. The pet, if a dog, often develops a rash or weeping sores. This can progress to hair loss, hyperpigmentation of the skin, thickening of the skin, and foul odor. The lesions in cats are different. Usually cats develop multiple small crusts (we call this miliary dermatitis). This can progress to hair loss (especially over the back), and sores (especially on the face).
Not all itchy pets have allergies. Other conditions including mite infestation, contact with irritants, dry skin, seborrhea, auto-immune diseases, yeast infections, fungal infections (ringworm), and bacterial infections of the skin can result in a pet that itches excessively. It is important for us to rule these other causes out and if they are present treat them before initiating diagnostics and therapy for allergic skin disease.
What can be done to stop the problem?
With allergies, the best approach is to eliminate the source of the allergy. With some types of allergies, such as food allergy, this can be a simple matter of identifying the offending food and eliminating it from the diet. There are now prescription diets designed with a molecular size of the protein so small they cannot act as a hapten (antigen which initiates the allergic response). These diets must be the ONLY food or other protein containing substance your allergic pet can eat or chew on to properly evaluate if food allergy is a significant component of your pets allergy. With other types of allergies, such as fleabite hypersensitivity, the offending agent can be eliminated, but much effort is required. Still other causes of allergies (allergens such as inhaled grass pollen or inhaled mold spores) are impossible to eliminate from the animal's environment.
If the cause can not be eliminated, then one can approach the problem in two distinct ways. One way is to treat the symptoms. The other is to desensitize the pet before the symptoms occur.
1. Treating the symptoms
Often when a pet is seen for itchy skin the first time the approach taken is to treat the symptoms.
This often starts with using medications called corticosteroids (prednisone, dexamethasone, triamcinolone, etc.) to stop the itching caused by inflammation. The term can be confusing as we often hear about “steroids” used as performance enhancing drugs. (This is an entirely different group (which includes testosterone, stanozolol, diabanol etc.) which builds muscle but has no effect on inflammation.) (It is not used to treat skin disease.) Corticosteroids have a very rapid anti-inflammatory effect. They can be used safely for short periods of time in otherwise healthy pets. Frequently even when used this way the pet will have increased thirst and increased appetite and often urinates both more volume and more frequently. This group is not a good choice for long term permanent use as there can be many undesirable side effects with frequent long term use.
A second medication often given is an antihistamine. Antihistamines work by blocking the attachment of histamine to cells that trigger inflammation. Antihistamines must be given before inflammation occurs to be effective. Since biological chemicals other than histamine play a significant role in dog and cat skin allergy of pets, it is usually not effective to use antihistamines as the only medication. Sometimes they are coupled with other medications to improve the reduction of the itching.
C. Fatty Acids
Another group of drugs used to treat skin allergy is the essential fatty acids. Certain fatty acids block inflammation by interfering with a group of chemicals known as prostaglandins. Research has shown about a 30% reduction in inflammation associated with using essential fatty acids. It is important to know which fatty acids do this, since other fatty acids can promote prostaglandin production and make inflammation worse. We can dispense or recommend a suitable fatty acid supplement.
Cyclosporine, (trade name Atopica,) is sometimes used for long term treatment of allergic skin disease. Atopica is a selective immune suppressant drug. It originally was used in transplant patients to help prevent rejection of the transplanted organ. It was tested and has been used at a much smaller dose to effectively treat dogs with atopic dermatitis. While prednisone has many potential long term adverse side effects, cyclosporine has had fewer. Some animals do have undesirable symptoms when Atopica is started. This can include gastrointestinal signs of vomiting or diarrhea; and much less commonly muscle cramps, loss of appetite, or inflammation of the gingival tissue of the mouth. These side effects reverse quickly if the medication is stopped. For the majority of dogs that do not develop these problems, Atopica can safely be used long term. Initially the medication is given every day for 4 to 8 weeks. Once symptoms have resolved, the frequency can be reduced to once every 3 to 4 days or sometimes even less frequently. While this medication helps many dogs with allergic skin disease, there are also many that do not improve. If there is not a beneficial effect in 8 weeks the medication should be stopped. It is also important to know that there are different forms of Cyclosporine and unfortunately the less expensive form is not adequately absorbed from the intestine of our patients. This is why some dogs well controlled with Atopica become symptomatic when changed to generic cyclosporine.
One new medication available for treating allergic skin disease is Oclacitinib (Trade name Apoquel.) This is a rapidly acting effective medication to reduce the symptoms of allergic skin disease. It works through a different chemical mechanism that the other anti-inflammatory medications previously being used. It inhibits Janus kinase which has been shown to be a significant contributor to inflammation associated with allergic skin disease. Since this is still a relatively new medication, we do not know all of the side effects that may occur. The product is labeled only for pets over 12 months of age and is contraindicated if there is any neoplasia (cancer), or any significant infection of the lungs, ears, or feet. Currently we are recommending this product for pets that have recurring episodes of pruritic skin disease.
F. Monoclonal Antibody therapy
Another new therapy is a monoclonal antibody that id designed to target and neutralize cytokine IL-31. This is a key itch-inducing cytokine in canine atopic dermatitis. This interrupts the itch cycle, and allows the dogs to stop scratching so damaged skin can heal. We utilize CYTOPOINTTM which is given as a subcutaneous injection that can be repeated once a month if necessary.
2. Topical medications
Finally, there are many medications that can be applied to the skin to reduce inflammation directly or indirectly by helping clear up complications of inflamed skin. These products come in many forms: shampoos, lotions, ointments, rinses, sprays, etc. They include topical anesthetics, soothing compounds such as oatmeal, hypoallergenic shampoos, corticosteroids, moisturizers, antibacterial compounds, anti-yeast compounds, etc. Which products are to be used is based on the Veterinarians assessment of the skin.
3. Treating secondary conditions
Secondary conditions such as bacterial infection of the skin, yeast or fungal infection, parasites, and trauma will also need to be treated. This is done with antibiotics, antifungals, miticides, insecticides, and other medication based on the pets condition. Flea prevention medications are a very important member of this group. Currently several of the older flea preventive medications are not effective in quickly removing and keeping fleas off our pets. There are currently no effective dips, powders, nor sprays. For this reason we are recommending the new tablet medications as they are working far better. Two that we often recommend are Nexgard and Bravecto.
4. Food trial
Food allergy contributes to about 30% of allergic skin disease. Contrary to much internet and marketing information, no one food nor group of foods is responsible for food allergy. Rather, it is more individualized. One dog may indeed be allergic to grains and benefit from their elimination from its diet. On the other hand another may be allergic to lamb, chicken, or potatoes. The only way to identify whether a food allergy is present is by using a food elimination trial. Originally this meant feeding a novel protein diet which had one animal protein and one plant protein, neither of which the pet had previously eaten. At that time there were very few food items used in pet food. Today there are a very large number of different protein sources that can be found in pet food. This makes it much more challenging to find a diet with protein sources the pet has never been exposed to. For this reason, when we suspect food allergy is contributing to the pets itchiness, we use hydrolyzed “zero antigen,” diets. When this is done, a prescription diet designed for this purpose is dispensed and you will be instructed to not allow any other food, treats, or other items to be eaten or picked up and swallowed for at least 60 days. If food is a major contributing factor, the symptoms will go away and continue to not be present even as other medications/treatments are discontinued. At this point we have the options of trying what we think would be a novel protein diet for the individual (based on historical information regarding what it has eaten in the past,) or alternatively to keep feeding the hydrolyzed diet.
Another approach has been made available by recent breakthroughs in allergy testing. Historically the only way to test for skin allergy was intradermal testing, in which small amounts of various antigens were injected into the dermis and evaluated for development of a wheal. This was, and continues to be a very good way to identify skin allergy, however when not done correctly it can result in both false positive and false negative results. In the last several years several testing protocols have been developed in which blood is drawn and submitted to a laboratory which then uses their test to identify which antigens the pet is reacting to. There are antibodies associated with allergy in the pet which react to antigens from the offending substance on the test. We at All Creatures Veterinary Hospital are currently using a blood test to identify which substances the animal is allergic to. We can test for inhalants (both indoor and outdoor), contact allergens, fleabite hypersensitivity, bacterial hypersensitivity, and food allergy. (The food allergy component of RAST testing is not considered reliable, so we prefer to use an elimination diet as described above, to rule out food allergy.) Such factors as when the allergy occurs (seasonal or not), where it occurs (indoors or outdoors), and what parts of the body are involved help determine which tests are most likely to be beneficial. Once the results of the testing are returned, we can determine what the best approach to treat the allergy is. If elimination of the cause is not practical, then desensitization is recommended. The solutions used for desensitization are prepared based upon the results of the blood test. These solutions contain very small concentrations of the offending substances. The desensitization process consists of a series of timed injections. The material injected is a dilute solution of the offending antigen. Each subsequent injection contains slightly more of the antigen. Initially the injections are given two days apart. As the concentration increases, the time between injections is increased, until at the maximum concentration used, the injections are given once per month.
The principle behind desensitization is that certain antibodies (called IgG antibodies) are produced by normal animals, whereas an undesirable type of antibody (called IgE antibodies) are produced by animals that suffer from allergies. The IgE antibodies trigger the allergic reaction when they come in contact with the substance the animal is allergic to. The desensitization process increases the production of the beneficial IgG which is then able to tie up the offending antigen before it binds to IgE and creates the allergic reaction.
In practice, this desensitization results in dramatic reduction of the symptoms of allergy. Many of the pets we have desensitized have gone from being animals that are constantly chewing at themselves, having balding, smelly, irritated skin to being animals that have healthy skin and hair coats with only occasional scratching. They become happier pets, and are much more pleasant to have around. The additional benefit to desensitization is that you do not have to give medication to your pet constantly. This reduces the risk of side effects from the medications, and reduces the trouble you have in having to give medication, baths, etc. to your pet.
What is the next step?
If your pet is having signs suggestive of allergic skin disease, contact us and we can set up an appointment to evaluate your pet and let you know which approach would be best for your pet based on its history and current condition.
We are available for appointments Tuesday through Friday from 9:00 AM to 12:00 noon, and 3:00 PM to 6:00 PM, and Saturdays from 9:00 AM to noon and 2 PM to 5 PM. The receptionist can make an appointment when you call during office hours.
Robert L. Linville, DVM
Rev. July 19, 2017