Atopy in Cats


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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

    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:

  • Antihistamines

  • 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).

    Home Care

    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.

    Preventative Care

    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.

    • Skin testing (or occasionally blood testing) to determine specific allergens to which your cat may be allergic.

    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.

  • 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.

    This test usually requires referral to a veterinary dermatologist. Animals must be off all medications before testing so that the skin can react properly to the antigenic challenge of the allergen injections. Reactions to allergens in cat skin are subtle and therefore more difficult to interpret.

  • Two primary forms of treatment for atopy are available: drug treatment and immunotherapy. The ideal treatment for most moderately and severely affected animals 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 cats with atopy are young and may require years of therapy. Treatments for atopy may include one or more of the following:

  • Antihistamines are much less helpful in atopic cats than they are in humans. Antihistamines help only 25 to 30 percent of atopic cats, but often are tried first because they have fewer adverse effects than do the cortisone-like drugs (i.e., corticosteroids). 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 cat.

  • Fatty acid supplements may relieve itchiness (i.e., pruritus) 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 (i.e., prostaglandins) 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 cats that do not respond well to antihistamines may respond to a combination of antihistamines and fatty acids.

  • Secondary bacterial infections are common in cats with allergic skin disease. Therefore, cats 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 (i.e., pruritus) 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 (i.e., pruritus).

  • 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. Cats can experience severe adverse effects if corticosteroids are not used carefully. Examples of the adverse effects of corticosteroids include increased water consumption (polydipsia) and urinations (polyuria), increased appetite and food intake (polyphagia) 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. Long-acting injectable corticosteroids should be reserved for use in cats that resist administration of oral medications.

  • Immunotherapy (hyposensitization, desensitization, allergy shots) theoretically is the ideal form of treatment for atopy, and is recommended for cats 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 percent of atopic cats.

    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 may then be maintained for a relatively long period of time. Improvement is gradual and your cat 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.

    Atopy varies considerably in intensity depending on the individual animal and its environment. Therefore, home monitoring and close communication with your veterinarian are vital for success. Treatment is most likely to be effective if individualized to the patient. Follow-up for atopy may include the following:

  • Administer as directed all medications prescribed by your veterinarian. Treatment often fails because medications are stopped as soon as improvement is seen or before sufficient time has been allowed for improvement to occur. Administer medications for the full time period prescribed unless otherwise directed by your veterinarian.

  • Remember to have patience with immunotherapy. Immunotherapy should be tried for 9 to 12 months before concluding that it has been a failure.

  • Observe cats on immunotherapy for signs of increased itchiness (i.e., pruritus), hives or swelling after injections. Although uncommon, cats may react to the allergen extract. Alterations in the injection schedule may be helpful to alleviate these problems. Severe reactions (i.e., anaphylaxis) may be life-threatening, but fortunately are extremely rare.

  • Cats receiving immunotherapy may improve after one injection but begin to scratch before the next injection is due. Shortening the interval between injections may help. Always consult your veterinarian before making changes in the injection interval. Schedules may become complicated. Keep a log of how much extract was given and record the date of the injections.

  • Observe your cat for rashes, pustules, infected ears or any other skin lesions that may occur secondary to scratching. Flare-ups of these problems may occur while waiting for generalized improvement and will need to be treated appropriately.

  • Avoidance of allergens usually is impractical due either to the ubiquity of the allergen (e.g., house dust mites) or the large number of offending allergens. However, in-home air filters may be helpful.

  • Cats with seasonal atopy may not require medications during certain parts of the year. Close observation and good record-keeping may identify times when medications are not needed.

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