Veterinary care should include diagnostic tests and subsequent treatment recommendations.
Diagnostic tests are necessary to rule out other skin diseases, as well as to support the diagnosis of atopy. These tests may include:
- Your veterinarian will get a complete medical history of your dog. Expect to be asked about the age of onset, whether the problem is or was at one time seasonal and where your dog chews and scratches. Bring a record of which medications your pet has previously been taking and be prepared to answer questions about how effective they have been.
- Your veterinarian will perform a complete physical and dermatological examination. Included in the exam of the skin should be a careful exam of the feet, pads and claws. There will also be special attention paid to the ears. Atopy will sometimes present itself as recurring external ear infections without any other skin symptoms.
- A skin scraping will be done to help rule out scabies. Since these mange mites are notoriously difficult to find, your veterinarian may recommend a trial treatment for scabies to completely rule this disease out, especially if there is ear involvement. Atopy and scabies both commonly show ear symptoms.
- A fungal culture is often taken to rule out dermatophytes (ringworm fungi). Dermatophyte infections in the skin can mimic the symptoms of many skin diseases and thus, a culture is frequently a part of the diagnostic process.
- A food trial may be done to rule out food allergy. During a food trial, your dog is fed a food containing ingredients that it has never been exposed to before as its only source of food for six to 12 weeks. If the symptoms don’t improve, food allergy can be excluded.
- Once the above diseases have been ruled out, a presumptive diagnosis of atopy is made. Allergy testing is then performed to identify allergens to which your pet is sensitive. Intradermal allergy testing (skin testing) is done to determine which allergens will cause a reaction. The hair is clipped from one side of the thorax and small amounts of many individual allergens are injected into the skin. Light sedation may be necessary to allow proper restraint during the procedure. This test usually requires referral to a veterinary dermatologist, which may necessitate travel to the nearest specialty practice. Your pet must be off all medications prior to testing so that the skin will react. Reactions to allergens in cat skin are subtler and therefore, are more difficult to read. There is a blood test available for dogs to test for allergens by measuring the levels of IgE antibody to different allergens that are present in the bloodstream. IgE is the type of antibody that is involved in the allergic response. The advantage of this test is the convenience for the pet owner and the veterinarian. A blood sample is sent to one of several commercial laboratories. There is no need to travel to a dermatologist or to withdraw medications. However, false positive results are often a problem and this test is considered less reliable than skin testing. More accurate blood tests are being developed and this technique may be more viable in the future.
Two primary forms of treatment for atopy are available: drug treatment and immunotherapy. The ideal treatment for most moderately and severely affected dogs is some combination of both types of treatment. Drug therapy relieves the symptoms of atopy but does nothing to treat the underlying allergy itself. Most dogs with atopy are young and may require years of therapy.
Treatments for canine atopy may include one or more of the following:
- Antihistamines are much less helpful in atopic dogs than they are in humans. Antihistamines help only 25 to 30% of atopic dogs, but often are tried first because they have fewer adverse effects than do the cortisone-like drugs. Some animals respond better to one antihistamine than to others, and your veterinarian may try 2 or 3 different types of antihistamines before concluding that they are not helpful in a given dog.
- Fatty acid supplements may relieve itchiness by modulating the immune response. Certain fatty acids such as eicosapentanoic acid (found in fish oil) help change the chemical composition of cell membranes and ultimately the types of chemical mediators produced during the allergic response, resulting in a milder response. Like antihistamines, these products are not helpful in all affected animals, but they are very safe. Some dogs that do not respond well to antihistamines may respond to a combination of antihistamines and fatty acids.
- Secondary bacterial infections are common in dogs with allergic skin disease. Therefore, dogs with atopy occasionally need antibiotics to treat complicating pyoderma. Yeast infections of the skin and ear also have to be treated occasionally.
- Shampoo therapy may be very helpful in managing itchiness caused by atopy. Shampoos that contain colloidal oatmeal are soothing and moisturizing, and can be used frequently without drying the skin. Some oatmeal-based shampoos contain topical anesthetics or topical corticosteroids that are very safe and further help reduce itchiness.
- When the above treatments are no longer effective, corticosteroids such as prednisone may be used. This class of drugs is very effective in atopic animals. Unfortunately, however, these drugs have many potential adverse effects that restrict their long-term use. Examples of the adverse effects of corticosteroids include increased water consumption and urinations, increased appetite and food intake leading to obesity, suppression of the immune system leading potentially to secondary infections, irritation of the stomach, alterations in liver function tests, and suppression of normal adrenal gland activity. Short-acting, orally-administered corticosteroids are safer than long-acting injectable corticosteroids because the former can be cleared rapidly from the animal’s body in the event of adverse effects. Any dog that can be helped by long-acting injectable corticosteroids can be relieved just as effectively and with less risk by use of short-acting orally-administered corticosteroids.
- Immunotherapy (hyposensitization, desensitization, allergy shots) theoretically is the ideal form of treatment for atopy, and is recommended for dogs that cannot be managed safely and effectively with symptomatic therapy. The exact mechanism by which immunotherapy works is not well understood, but the goal is to induce tolerance by the immune system to allergens to which the animal is sensitive. This technique is effective in 60 to 80% of atopic dogs. An extract of the allergens selected by allergy testing is prepared. Initially, a small amount is injected frequently (every 1 to 2 days) and the dosage gradually increased. Due to the frequency of injections, your veterinarian usually will show you how to administer the injections at home. Once the cumulative dose reaches a certain level, the injection interval is slowly increased until injections are given every 2 to 3 weeks. The interval then may be maintained for a relatively long period of time. Improvement is gradual and your dog may not benefit markedly for the first 3 to 6 months of immunotherapy. Antihistamines, fatty acid supplements and soothing shampoos may be used while immunologic tolerance develops.
- Another therapy includes use of an immunomodulator drug called cyclosporine A (Atopica®, Novartis). Cyclosporine has properties that fight against inflammation and itching. It is generally started daily and often decreased to every other day or every third or forth day as clinical signs improve. It may take four to eight weeks to see improvement.
- A newer therapy called Oclacitinib (Apoquel) has been very effective in control of itching in dogs with allergies. This drug uniquely targets cytokines that are involved in the itch process. Onset of relief can be as early as 4 hours and controls the itch within 24 hours. Many veterinarians like this drug because it controls itching without the side effects of steroids.
- Atopy is a disease that varies considerably in intensity depending on the individual animal and his present environment. Therefore, home monitoring and communication with your veterinarian is vital for success. Treatment is most likely to be effective if individualized to the dog.