Overview of Feline Atopy (Cat Allergies)
Atopy is a pruritic (itchy) skin disease of animals that is caused by an allergy to substances in the environment that are contacted through the air, either by absorption through the respiratory tract or contact through the skin. Atopy is thought to be an inherited disease. It can be difficult to diagnose in cats and, therefore, is probably under-diagnosed.
Symptoms of atopy usually begin relatively early in life, often by one year of age. Symptoms usually are seasonal at first, with most cats showing clinical signs in the summer months when airborne allergens (such as plant pollens) are present in higher concentrations. As atopic cats age, their symptoms tend to become less seasonal as they become allergic to more substances. Eventually, their itchiness can occur year-round.
Cats with atopy are usually itchy, particularly the hands and feet. The skin may be red and irritated due to scratching, and the ears may also be inflamed. The symptoms of food allergy are difficult to distinguish from those of atopy.
What to Watch For
- Chewing at the paws
- Scratching the face or rubbing it on the ground or with the paws
- Scratching the ears
- Shaking the head
Veterinary Care for Atopy in Cats
Diagnostic tests are necessary to rule out other skin diseases, as well as to support the diagnosis of atopy. These tests may include:
- A complete medical history and perform a thorough physical examination, especially checking the ears and the skin of the face and paws. Often, abnormalities may not be detected on the physical examination of cats with atopy. Occasionally, redness between the toes or around the muzzle of the face is the only finding.
- Skin scrapings to eliminate other diagnoses such as demodectic or sarcoptic mange (caused by mites).
- Fungal culture to rule out ringworm (also called dermatophytosis).
- Skin testing (or occasionally blood testing) to determine specific allergens to which your pet may be allergic.
Initial treatments may alleviate symptoms, but do not treat the underlying cause of the allergy. Immunotherapy (allergy shots that work by modifying your cat’s immune response to allergens) is considered the best treatment for moderate to severe or long-standing cases of atopy.
Treatments may include one or more of the following:
- Fatty acid supplements
- Antibiotics to treat secondary pyoderma (bacterial infection of the skin)
- Soothing shampoos
- Corticosteroids (hormones) such as prednisone (very effective for reducing the symptoms of atopy, but have many potential side effects that can limit their long-term use).
NOTE: All of the above treatments alleviate symptoms, but do nothing to treat the underlying allergy.
For treatment of the underlying allergy:
- Immunotherapy (allergy shots that work by modifying your cat’s immune response to allergens; considered the best treatment for moderate to severe cases).
Atopy cannot be cured and most cats require some form of therapy throughout their lives. You will need to administer any medications prescribed by your veterinarian and avoid offending allergens as much as possible. Skin testing (also called allergy testing) can be performed to identify the specific substances to which your cat is allergic. As time goes by, however, most cats with atopy become allergic to more and more allergens, making avoidance impractical in the long run.
You should practice strict flea control. Other itchy (pruritic) skin diseases such as flea allergy dermatitis may have an additive effect on your cat’s skin condition.
Observe your cat for rashes and worsening of any skin lesions. Secondary bacterial infection of the skin (pyoderma) is common in cats with atopy and can contribute to their discomfort.
Since enviromental exposure to allergens is important in the development of disease, it cannot be prevented. Airborne allergens, such as plant pollens, are difficult to avoid, and there is little that can be done to prevent the development of atopy in a predisposed individual. Cats that grow up in low allergen environments (dry climate with high elevation) may be less likely to develop symptoms.
In-depth Information on Feline Atopy
Many skin diseases of cats feature pruritus (itching) as a symptom and may appear similar to atopy. Ruling out other causes of pruritus is an important part of establishing a diagnosis.
Diseases that can appear similar to atopy include:
- Food allergy. Food allergies in cats commonly causes a pruritic skin condition. Like with atopy, cats with food allergy often chew their feet, rub their faces and scratch their ears. Thus, the symptoms of food allergy are virtually indistinguishable from those of atopy. One important historical difference to remember is that atopy symptoms usually begin between one and four years of age, whereas food allergy can begin at any age. A cat that has an onset of signs, and is less than eight months of age or over six years of age, is unlikely to have atopy. Also, atopy is usually well controlled by treatment with corticosteroids (hormones) like prednisone. Food allergy is variably responsive to prednisone; only about 50 percent of affected cats will respond.
- Flea allergy dermatitis. This is the most common allergic skin disease seen in the United States. Like food allergy, it is variably responsive to corticosteroids. Cats with flea allergy tend to chew and scratch at their back ends, so lesions are typically seen over the rump, on the belly and between the hind legs. Some cats may also have lesions around the neck. This difference helps to differentiate this disease from atopy. It is possible, however, to see atopy and flea allergy in the same animal.
- Scabies. This itchy skin disease of cats is caused by the sarcoptic mange mite. Affected cats are extremely itchy and often have lesions on their ears, elbows and hocks. Lesions may also be seen elsewhere on the cat. This disease is poorly responsive to treatment with corticosteroids.
- Pyoderma. This bacterial infection of the skin is often associated with atopy and other pruritic skin diseases. Chronic self-trauma to the skin breaks down normal defense mechanisms and allows colonization by bacteria leading to infection. Infected skin can be very itchy. Some animals with atopy are only mildly itchy most of the time but may be much worse when they have pyoderma. Less commonly, yeast infections of the skin may be seen secondary to atopy and can also cause the animal to be itchy.
Diagnosis In-depth for Feline Atopy
Veterinary care includes diagnostic tests and subsequent treatment recommendations. Diagnostic tests are necessary to rule out other skin diseases as well as support the diagnosis of atopy.
- Your veterinarian will take a complete medical history about your cat. Important aspects of the medical history include the age of onset, whether the problem is (or was at one time) seasonal and which areas of the body your cat chews and scratches. Bring a record of medications your cat has received previously and be prepared to answer questions about how effective they have been.
- Your veterinarian will perform a thorough physical and dermatological examination of your cat. Included in the examination of the skin will be a careful examination of the feet, food pads and nails. Special attention will be paid to the ears.
- A skin scraping will be performed to eliminate scabies. The sarcoptic mange mites are notoriously difficult to find, even with repeated skin scrapings. Your veterinarian may recommend a trial treatment for scabies to rule out this diagnostic possibility, especially if the ears are severely affected from scratching.
- A fungal culture often is performed to rule out dermatophytosis (ringworm). Dermatophyte infections of the skin can mimic many other skin diseases, and a fungal culture frequently is part of the diagnostic process.
- A food trial may be recommended to rule out food allergy. During a food trial, the animal is fed a food containing ingredients that it has never been exposed to before as its only source of food for 6 to 12 weeks. If the symptoms don’t improve, food allergy is excluded as a diagnostic possibility.
- Once the previously described diseases have been ruled out, a presumptive diagnosis of atopy is made. Allergy testing is then performed to identify allergens to which the animal is sensitive. Intradermal allergy testing (skin testing) is done to determine which allergens cause a skin reaction. The hair is clipped from one side of the chest and small amounts of many different allergens are injected into the skin. Light sedation may be necessary to allow proper restraint during the procedure.