One of the most common medical complaints that we see in our office is dogs with skin infections, “hot spots”, or allergic dermatitis, also known as atopic (atopy) dermatitis. Unlike people who react to allergens most commonly with nasal symptoms and/or hives, dogs react with skin and/or gastrointestinal problems. This is because there are a higher proportion of mast cells, which release histamines and other vasoactive substances in the face of an allergic challenge, in the skin of dogs. These problems may range from poor coat texture or hair length, to itching and chewing, to hot spots and self-mutilation, gastrointestinal pain and discomfort, diarrhea, and flatulence. Allergies may also play a part in chronic ear infections. The most common causes of canine allergic dermatitis are flea allergy, food allergy, inhalant or contact allergy, and allergy to the normal bacterial flora and yeast organisms of the skin. To make matters more difficult to diagnose and treat, thyroid disease may add to the problem as well.
Canine atopic dermatitis (allergic dermatitis, canine atopy) is an inherited predisposition to develop allergic symptoms following repeated exposure to some otherwise harmless substance, an “allergen”. Most dogs begin to show their allergic signs between 1 and 3 years of age. Due to the hereditary nature of the disease, several breeds, including Golden Retrievers, most terriers, Irish Setters, Lhasa Apsos, Dalmatians, Bulldogs, and Old English Sheep dogs are more commonly atopic, but many dogs, including mixed breed dogs can have atopic dermatitis. Atopic animals will usually rub, lick, chew, bite, or scratch at their feet, flanks, ears, armpits, or groin, causing patchy or inconsistent hair loss and reddening and thickening of the skin. The skin itself may be dry and crusty or oily depending upon the dog. Dogs may also rub their face on the carpet; ear flaps may become red and hot. Because the wax-producing glands of the ear overproduce as a response to the allergy, they get bacterial and yeast (Malassezia ) infections of the ear.
In order to overcome these frustrating symptoms, your veterinarian’s approach needs to be thorough and systematic. Shortcuts usually will not produce results and only add to owner frustration and canine discomfort.
Inhalant and Contact Allergies
Substances that can cause an allergic reaction in dogs are much the same as those that cause reactions in people including the pollens of grasses, trees and weeds, dust mites, and molds. A clue to diagnosing these allergies is to look at the timing of the reaction. Does it happen year round? This may be mold or dust. If the reaction is seasonal, pollens may be the culprit.
Many people don’t suspect food allergies as the cause of their dog’s itching because their pet has been fed the same food all its life and has just recently started having symptoms. However, animals can develop allergies to a substance over time, so this fact does not rule out food allergies. Another common misconception is that dogs are only sensitive to poor quality food. If the dog is allergic to an ingredient, it doesn’t matter whether it is in premium food or the most inexpensive brand on the market. One advantage to premium foods is that some avoid common fillers that are often implicated in allergic reactions.
This type of reaction usually is not to the flea itself, but rather to proteins in its saliva. Interestingly enough, the dogs most prone to this problem are not dogs who are constantly flea ridden, but those who are exposed only occasionally! A single bite can cause a reaction for five to seven days, so you don’t need a lot of fleas to have a miserable dog.
Bacterial hypersensitivity occurs when a dog’s immune system overreacts to the normal Staphylococcus (Staph) bacteria on its skin. It appears that bacterial hypersensitivity in the dog is more likely to occur if other conditions such as hypothyroidism, inhalant allergy, and/or flea allergy are concurrently present. Bacterial hypersensitivity is diagnosed through bacterial culture and examination of a biopsy sample. Microscopically, there are certain unique changes in the blood vessels of the skin in bacterial hypersensitivity.
Allergy testing is the best diagnostic tool and the best road to treatment for dogs that are suffering from moderate and severe allergies. There are several different testing methods available. The most common is a blood test that checks for antigen induced antibodies in the dog’s blood. Intradermal skin testing may also be performed. In this method of testing, a small amount of antigen is injected into a shaved portion of the dog’s skin. This is done in a specific pattern and order so that if the dog shows a small raised reaction, the offending antigen can be identified. After a period of time (hours), the shaved area is examined to detect which antigens, if any, created a reaction. Allergy testing is performed to develop a specific therapy for the allergic animal.
Many medicated shampoos have compounds in them that are aimed at soothing injured skin and calming inflammation. In addition, frequent bathing (weekly to every other week) of the dog can remove allergens from the hair coat, which may contribute to skin allergy flare-ups. The medicated baths we recommend are those that actually contain antimicrobial and antifungal agents as well as ingredients that allow the skin to be bathed on a more frequent basis without drying it out. Application of a rinse afterwards also helps to prevent drying out of the skin and hair coat.
Antihistamines can be used with good safety in dogs. About one third of owners report success with antihistamines. These medications tend to have a variable effect between dogs. For some allergic dogs, antihistamines work very well in controlling symptoms of allergic skin disease. For other dogs, very little effect is seen. Therefore, a minimum of three different types of antihistamines should be tried before owners give up on this therapy. Examples of antihistamines commonly used for dogs include Benadryl, Chlortrimeton, Atarax, Claritin, Zyrtec, and Clemastine. However, antihistamines are considered to be worth trying in most cases since the side effects associated with antihistamines is low, and they are typically inexpensive medications.
Antibiotics and Antifungal Medications
Antibiotics are frequently needed to treat secondary skin infections. Anti-fungal medications are frequently needed to treat secondary yeast infections.
For dogs with this problem, a strict flea control regime must be maintained. The best flea control options include the use of products such as Advantage, Revolution, Frontline, Comfortis, and Sentinel.
The Omega-3 and Omega-6 essential fatty acid supplements work by improving the overall health of the skin. These fatty acids are natural anti-inflammatory and anti-oxidative agents. They reportedly are helpful in 20% of allergic dogs. My own experience puts this figure a little higher. They are certainly worth a try because they are not harmful and have virtually no side effects. Omega-3 fatty acids are found in fish oils and omega-6 fatty acids are derived from plants containing gamma-linolenic acid (GLA). These supplements are different from those sold to produce a glossy coat. Products that contain both omega-3 and omega-6 fatty acids include Allergen Caps and Halo.
Allergies develop through exposure, so most hypoallergenic diets incorporate proteins and carbohydrates that your dog has never had before. As mentioned previously, the quickest and best way to determine which foods your dog may or may not be allergic to is through diagnostic allergy testing. As dairy, beef, and wheat are responsible for 80% of food allergies in dogs, these items should be avoided. Novel protein sources used in hypoallergenic diets include venison, egg, duck, kangaroo, and types of fish not usually found in pet food. Carbohydrate sources include potatoes, peas, yams, sweet potatoes, and canned pumpkin.
Hydrolyzed protein diets are diets in which the protein source has been synthetically reduced to small fragments. The theory behind feeding a hydrolyzed protein source is that the proteins in the food should be small enough that the allergic dog’s immune system will not recognize the protein fragments and will not mount an immune response resulting in an allergy.
Most pets with food allergies respond well when switched to a store-bought hypoallergenic diet, but occasionally an animal suffers from such extreme allergies that a homemade diet is the only option. In this case, the diet should be customized with the aid of a veterinarian.
Corticosteroids and Immunosuppressive Agents
Cortisone products such as prednisone, prednisolone, and dexamethasone reduce itching by reducing inflammation. These medications are not without side effects, so they need to be used judiciously in treating skin allergies. Steroids should be considered only when the allergy season is short, the amount of drug required is small, or to relieve a dog in extreme discomfort. Side effects can include increased thirst and appetite, increased need to urinate, and behavioral changes. Long-term use can result in diabetes and decreased resistance to infection. In some dogs, long term, low-dose alternate day therapy is the only management protocol that successfully controls the atopic pet. This protocol should be used only as a last resort after all other methods have been exhausted to avoid the potential long-term complications of the medication.
Cyclosporine (Atopica) is a medication, which seems to be fairly effective at reducing the inflammation associated with skin allergies and calming the immune system of the affected dog. However, the pricing of cyclosporine may be prohibitive for larger breed dogs.
Allergy shots are very safe, and many people have great success with them; however, they are very slow to work. It may be six to twelve months before improvement is seen. Once the allergens for the dog are identified, an appropriate immunotherapy is manufactured for that specific dog, and treatment can begin. After the offending antigens are identified, then a mixture of these antigens can be formulated into a hyposensitizing injection. Depending on the type of agents used, these injections will be given over a period of weeks to months until the dog or cat develops immunity to the agents. After initial protection, an occasional booster may have to be given.
If you know which substances your dog is allergic to, avoidance is the best method of control. Even if you are desensitizing the dog with allergy shots, it is best to avoid the allergen altogether. Molds can be reduced by using a dehumidifier or placing activated charcoal on top of the exposed dirt in your house plants. Dusts and pollens are best controlled by using an air cleaner with a HEPA filter. Air conditioning can also reduce circulating amounts of airborne allergens because windows are then kept closed.
Healthy skin and a normal hair coat are the result of many factors, both external and internal. There are several glands in the body responsible for the production of hormones that are vital for the regulation of other body functions as well as a normal skin surface and hair coat. Hypothyroidism may result in poor skin and hair coat, including hair loss or abnormal hair turnover, dull or brittle hair, altered pigmentation, and oily or dry skin. A blood test is the simplest and most direct way to tell if your dog is hypothyroid. Thyroid testing may include all or part of the following:
Baseline T4 Test or Total T4 (TT4): This is the most common test. Dogs with a failure of the thyroid gland will have a lowered level of the T4 hormone. However, there are other conditions that can cause the T4 to decrease, so if this test comes back positive for hypothyroidism your vet should recommend an additional blood test, either the T3 Test or the Baseline TSH test.
Baseline TSH Test: Measures the level of Thyroid Stimulating Hormone. In combination with the T4 or T3 test, it provides a more complete picture of the hormonal activity of your dog’s thyroid gland.
Free T4 by RIA (radio immunoassay): The Free T4 test using RIA techniques does not appear to be more or less accurate than the above TT4 test.
Free T4 by ED (equilibrium dialysis): This test may provide more accurate data on the level of T4 hormone in your dog’s bloodstream.
Baseline T3 Test: In combination with the T4 or TSH test, these two blood tests can give a clearer picture of the hormone levels found in the bloodstream. This test is not reliable when used alone. The T3 Test should always be given in combination with one of the other blood tests.
TSH Response Test: In this test, the veterinarian takes an initial measurement of the thyroid hormones in your dog’s bloodstream and then injects Thyroid Stimulating Hormone (TSH) into the vein. After 6 hours, a blood sample is drawn and the level of T4 is checked. If your dog has hypothyroidism, the level of T4 will not increase even after the TSH is injected. This is an expensive test and is being used less often due to decreased production by the manufacturers.
Hypothyroidism is treated with a daily dose of synthetic thyroid hormone called thyroxine (levothyroxine). Blood samples will need to be drawn periodically to assess the effectiveness of the dosage and make any adjustments necessary.
Successful management of the atopic, allergic dog is sometimes complicated and frustrating because multi-modal management is necessary in the majority of cases to control the allergic flare-ups. Proper diagnosis by a veterinarian and owner compliance and follow up care is essential to maximize the chances of curing or at least controlling the severely affected allergy patient.
The Animal Medical Center of Southern California is devoted to providing the best medical, surgicalm and emergency critical care available in veterinary medicine. As important as our medical expertise is, we believe that excellent care combines state-of-the-art veterinary medicine and surgery with a focus on compassion and respect for your pet and for your family.
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