What is atopic dermatitis?
Atopic dermatitis (atopy) is a common cause of skin problems in cats. When a cat with allergies encounters an environmental protein to which it is allergic, it sets off a reaction leading to skin problems. While the incidence of atopy is hard to define due to challenges in diagnosis, approximately 10-15% of cats treated by veterinary dermatologists are diagnosed with atopy.
What causes atopy?
Cats with atopy are often allergic to the same allergens that tend to affect humans: tree pollens, grass pollens, weeds, molds, and dust mites. While these allergens cause watery eyes and a runny nose in humans, cats respond differently and often develop skin inflammation in response to these allergens.
Although there are certain breeds of dogs that are predisposed to atopy, there are no known breed predispositions in cats. Atopy can develop at any age; the onset of new cases of atopy has been reported in cats as young as six months and as old as 14 years.
What are the signs of atopy?
Affected cats often have a history of chronic or recurrent itching, which may be seasonal or non-seasonal. Cats with atopy also tend to have a history of recurring skin and/or ear infections. In many cases, affected cats are so itchy that they create significant trauma to their skin. Affected cats may have severe scratches or abrasions, large areas of fur that have been licked away or pulled out in clumps, and color changes to the skin due to chronic licking and inflammation.
How is atopy diagnosed?
Your veterinarian will begin with a thorough physical examination of your cat. Your veterinarian will also take a complete patient history, asking you a variety of questions about your cat’s skin disease to better characterize the condition. From the physical exam and history, your veterinarian may begin to suspect atopy as the cause of your cat’s skin disease.
Unfortunately, there is no definitive test for atopy. It is a diagnosis of exclusion, meaning that your veterinarian will rule out other, similar skin conditions to arrive at a diagnosis. The signs of atopy are identical to many other skin diseases. Your veterinarian will likely perform tests to rule out skin parasites (e.g., fleas, mites, lice), bacterial skin infections, and ringworm. Biopsies may be performed to rule out autoimmune skin disease and other conditions. Your veterinarian may also recommend a food trial to rule out food allergy as a source of your cat’s skin issues. Ruling out other skin conditions is essential to arrive at a diagnosis of atopy.
"Ruling out other skin conditions is essential to arrive at a diagnosis of atopy."
Your veterinarian will also likely perform tests to assess your cat’s overall health. These tests will help rule out underlying medical conditions and determine whether your cat can be safely treated with medication. Laboratory tests will likely include a complete blood cell count (CBC), serum biochemical profile, and urinalysis.
There are certain tests, however, that can help guide the management of atopic dermatitis:
Intradermal allergy testing. This test involves injecting very small amounts of many different allergens into your cat’s skin and monitoring your cat’s immune response to these substances. This test can help determine which allergens your cat reacts to most strongly, which can help guide treatment.
Serologic allergy testing. Like intradermal testing, serologic allergy testing aims to determine which allergens are triggering your cat’s allergies. This test is performed on your cat’s blood. Serologic testing is generally considered less reliable than intradermal testing; however, it is often less expensive and does not require sedation, making it a viable option in some cases.
How is atopy treated?
There is no single best treatment for the management of atopy in cats. Allergies are managed, not cured, and therefore the optimal method of management varies depending on the individual patient and owner.
For cats with chronic skin inflammation from atopy, several management options exist. Some cats can be managed with daily low doses of immunosuppressive drugs, such as prednisolone or cyclosporine (Atopica®), although these medications may have side effects. Omega 3 and 6 fatty acids may also be helpful in some cats. Antihistamines are also tried sometimes, although they appear to be relatively ineffective for cats that are already suffering from itchiness.
Atopic cats may also benefit from allergen-specific immunotherapy, or allergy shots, which involves giving the cats injections or oral drops of very small amounts of substances they are allergic to (as determined by intradermal or serologic allergy testing) to build up their immune tolerance. This process takes time to help patients, with benefits often not apparent until three to twelve months (or more) of treatment. The statistics for improvement with allergen-specific immunotherapy show it is effective in approximately 60% of cats.
"Depending on the allergen, there may also be environmental measures that can be taken to decrease exposure."
Depending on the allergen, there may also be environmental measures that can be taken to decrease exposure. For example, a cat who is allergic to dust mites may benefit from changes in household cleaning practices. Cats allergic to food storage mites should be changed from a dry diet to a canned grain-free hypoallergenic diet, which will not contain these mites.
In many cats, their skin issues only flare up periodically. This is often the case in cats who are only allergic to a small number of allergens, resulting in a brief 'allergy season'. In these cases, a short course of oral prednisolone or even a steroid injection may fully resolve their skin problems and keep them comfortable until the next allergy flare-up. Many owners appreciate the convenience of steroid injections; however, it is important to note that long-acting steroid injections (Depo-Medrol®), especially repeated injections, can have side effects, including the development of heart failure and diabetes.
If your cat has a secondary skin or ear infection caused by allergies, this will also require treatment. Skin infections are often treated with oral or injectable antibiotics. Ear infections will likely be treated with drops applied to the ears.
What is the prognosis for atopy?
Unfortunately, the signs of atopy tend to worsen with age. Once your cat has been diagnosed with atopy, it is safe to assume that your cat will require lifelong treatment to manage her atopy and resulting secondary infections. Fortunately, there are a variety of medical treatments available for atopy, with new drugs constantly being developed. Therefore, it is typically possible for atopic cats to have a good quality of life with ongoing care.
