Atopy
General information
Other common/scientific names: atopic dermatitis, allergic dermatitis, allergic inhalant dermatitis, atopic disease
Atopy is an allergic disease in which a cat develops an allergy to substances in its environment that the cat inhales or absorbs through its skin. These substances, called allergens, do not cause problems in cats that do not have the disease.
Atopy is the second leading cause of allergic skin disease in the cat (behind flea bite allergies).
Causes
Cats that develop atopy have a genetic predisposition to become allergic to normally harmless substances in the environment, such as pollens (from grasses and trees), molds, and house dust mites. Repeated contact with these substances causes an allergic response in these cats. Because repeated exposure to an allergen is required before the allergic response will occur, cats will rarely show signs of atopy before six month of age, with the majority of cases showing up between 1-3 years of age (although older cats may also develop the disease).
Cardinal symptom
Itchiness
Symptoms
The most common symptom seen with atopy is intense itchiness. Often the cat is very itchy around its face, ears and neck, or on its abdomen and inner or outer thighs. Some cats are itchy all over. Hair loss, scratches, sores and scabs caused by self-trauma may be seen, and the skin may be secondarily infected by bacteria or yeast. Small raised lesions and crusts (called military dermatitis) may be seen over much of the cat’s body, especially around the neck or along the back. Redness of the skin is frequently noticed, and in some cases, eosinophilic placques and linear granulomas are seen as well. Often ear infections and eye infections are also present. Cats that are itchy on their abdomen and thighs frequently lick and chew to the point where very little hair is seen in these areas.
Note that the observed signs may be seasonal or nonseasonal, depending upon the particular allergen involved. However, many cats that begin by having seasonal atopy will become allergic to more and more allergens until they become allergic year-round.
Diagnosis
To make a diagnosis of atopy the veterinarian will first want to eliminate other common diseases that could cause similar clinical signs. Fleas, mites and other external parasites will need to be excluded as the underlying cause of the itchiness, as will ringworm. Skin scrapings and fungal cultures may be recommended to eliminate some of these other causes of itchiness. If a food allergy is suspected, an elimination food trial may be recommended.
Evidence which may support a diagnosis of atopy is seasonal itchiness, although some cases of atopy may cause itchiness all year long.
Intradermal skin testing or serum testing may be recommended to help with the diagnosis and treatment of atopy. Intradermal skin testing involves shaving the lateral chest of the cat and injecting small amounts of different allergens under the skin. By measuring the amount of reaction within the skin for each allergen, the specific offending allergens for that cat may be identified. Once the offending allergens have been identified, appropriate immunotherapy (or hyposensitization) injections may be recommended for treatment.
Serum testing to identify the offending allergens by using a blood sample is also available, and may also be used to develop appropriate immunotherapy injections for treatment. While much more convenient than intradermal skin testing, serum testing is not yet considered to be as reliable as intradermal skin testing.
Treatment
Unfortunately, atopy cannot be cured. Unless the offending allergens can be avoided, some form of treatment is often needed for the life of the cat. Several different treatment approaches are available, and are often used in combination with one another:
•Antihistamines (usually given orally) may decrease inflammation and itching in some cats with atopy. They are typically less effective at reducing itchiness than corticosteroids. However, if antihistamines are effective, the use of corticosteroid treatment may be avoided or used at a reduced dosage. Drowsiness or nervousness is sometimes seen with this medication. Antihistamines are often more successful if given in combination with essential fatty acids.
• Corticosteroids, potent immunosuppressives, are often effective for controlling the itchiness associated with atopy. However, because their long-term use can have severe side-effects, these drugs are typically given for short-term relief and are reduced to the lowest dosage that effectively controls the itchiness. This medication may be given orally or by injection.
• Cyclosporin is another immunosuppressive drug that can also be very successful at reducing itchiness. It is given orally, and does not have the severe side-effects with long-term use that are often seen with corticosteroids. However, unlike corticosteroids, it does not reduce itchiness right away. This medication may need to be given for a month or more before its effects are seen. Cyclosporin may be given in combination with corticosteroids, antihistamines and/or essential fatty acids.
• Essential fatty acids given orally as a capsule or liquid, or included in some commercial diets, may decrease the production of substances that help promote inflammation and itchiness in atopy. Often the dose of other medications can be reduced if essential fatty acids are given.
•Topical therapies are also useful in some cases. Bathing in tepid water may help cool and rehydrate the skin, as well as remove allergens from the fur. Colloidal oatmeal shampoos, medicated shampoos, or topical sprays may also be recommended to help soothe the skin.
• Immunotherapy, or hyposensitization, involves giving injections under the skin of gradually increasing doses of the offending allergens. The allergens selected are based on the results of intradermal or serum testing. If successful, these injections will reduce the cat’s sensitivity to the offending allergens. This form of therapy may ultimately succeed in 60-80% of cats, but it may take up to a year for a successful response to be seen. If the injections are successful, maintenance injections are needed every 1-3 weeks, usually for the life of the cat. Immunotherapy is typically considered when the cat has a very long allergy season, or when the cat has not responded well to other forms of treatment.
Unfortunately, there is no one treatment regime that works for all cats. Often various treatments, or combinations of treatments, must be tried until a satisfactory result is achieved.
Note that if a cat has a secondary bacterial or yeast infection, this must also be appropriately treated.
Prognosis
Atopy cannot be cured, and often worsens over time. Some form of therapy may be needed for the rest of the cat’s life. However, with individualized treatment and diligent care, over 90% of cases can be managed to allow the cat a high quality of life.
Prevention
If the specific allergens responsible for the allergic response have been identified through allergy testing, exposure to these allergens should be reduced as much as possible. Unfortunately, often the exact allergen or allergens responsible have not be identified or, even more frequently, cannot be avoided.
Also, cats with one sort of allergy often have other types of allergies. About 20-30% of cats with atopy also have a food allergy or a flea allergy. It appears that a cat may not show any symptoms until the collective total of its exposure to allergens reaches some critical threshold level. Once this level is exceeded, it will begin to have symptoms. For this reason, preventive measures should be taken to try and keep a cat from exceeding this threshold. An example of this is regular, effective internal and external parasite control.
Tips
While trying to find the best treatment plan to reduce itchiness in your cat, an Elizabethan collar may be necessary to prevent self-trauma to its head, face and ears.
If allergy testing is going to be done, make sure to discuss with your veterinarian which medications your cat can be on before the test. Allergy testing can be affected by a variety of medications, and your cat may need to be off certain medications for several weeks before the test is done in order to get the most accurate results.