Atopy

Atopy, or inhalant or contact allergy, is a common problem in cats. An ‘allergy’ is a hypersensitivity to a substance known as an allergen. Common allergens include house dust, pollens, dander, grasses, trees, and fabric.  Any airborne particle can potentially be an allergen. Although cats can show signs of respiratory allergies, more commonly skin problems occur. Symptoms may include: hair loss, skin redness, itchiness, and/or skin rashes or scabbing (known as miliary dermatitis).

Features of Atopic Dermatitis

• Seasonal pruritus (itchiness). After several years, the duration of the itchy period may lengthen so that the cat is pruritic year-round.
• Pruritus tends to begin early in a pet's life (between ages 1 to 3).
• Pruritus responds rapidly to cortisone-type medications (prednisolone, dexamethasone, and methylprednisone) or other immunosuppressant medications.

Diagnostic Testing

Because atopic dermatitis may look extremely similar to other causes of skin problems (flea allergy, ringworm, parasites), tests to rule out these diseases may be recommended: flea treatment, fungal testing, or skin cytology. After ruling out these issues, a food trial may be recommended to rule-out a food allergy, which is another common source of allergies in cats. If these tests are negative, your veterinarian may then recommend testing to identify specific allergens that your cat is sensitive to:

• HESKA blood test: Checks for the presence of antibodies to specific allergens specific to the Northwest and house dust or storage mites. Allergy shots may then be specifically formulated to the cat’s needs based on the test results (see below).
• Intradermal skin test: Requires a referral to a veterinary dermatologist. This test is similar to that performed on people. Small amounts of allergen are injected into the dermis of the skin. Inflammation or swelling of the skin is considered a positive response. Also, can be used to formulate allergy shots.
• Biopsy: In some cases, a tissue sample may be submitted for analysis by a pathologist.

Treatment Options

Depending on the severity of the allergy and response to treatment, your veterinarian may make several therapeutic recommendations.

Fatty Acid Supplements—These products are NOT analogous to adding oil to the pet's food. Instead, these special fatty acids act as medications, disrupting the production of inflammatory chemicals within the skin. They are often used in conjunction with antihistamines.

Antihistamines—Only about 30% of cats respond to antihistamines, but side effects are less common that with steroids. You may have to try several different antihistamines to determine which works the best for your cat. Cats that do not respond completely to antihistamines alone may do well on a lower dose of steroid when used in combination with antihistamines.

Antibiotics—Bacterial infections of the skin may occur due to chronic skin inflammation or from trauma from scratching.

Prednisolone (and other steroids)—These cortisone-type medications reduce inflammation of the skin by blocking production of inflammatory substances within the body. At the beginning of treatment, steroids may be administered at a high dose to induce a more rapid response. The dose will then be tapered down to the lowest dose possible to try to avoid potential side effects.

Potential Steroid Side Effects (associated with high doses/long-term use)

Anticipated/‘Acceptable’ side effects

• Increased thirst
• Increased appetite
• Increased urination or larger urine volume

'Unacceptable' side effects

• Immune suppression: upper respiratory infections, urinary tract infections
• Diabetes mellitus- which may resolve after steroids are discontinued
• Congestive heart failure- if heart disease is present

In some cases, injectable long-acting steroid injections may be administered. Because these injections last several days to several months, the potential for negative side effects may be increased. Therefore, we often try to use other means of steroid administration before injection.

Alternatives to Steroids
In some cases, a different immunosuppressive drug may be prescribed. Cyclosporine is a drug that modulates the abnormal immune reaction in atopic animals. It is used in cats when other treatments have failed or in those cats that cannot tolerate steroids. It is a relatively expensive medication compared to steroids but is not associated with as many side effects.

Hyposensitization (Allergy Shots)
Hyposensitization shots are a form of immunotherapy in which increasingly larger doses of allergens are injected into the body to induce hyposensitization, or immune tolerance. Repeated exposure to antigens will stimulate the immune system to produce more antibodies to the antigens. After a while, enough antibodies are produced so that exposure to the allergen will produce fewer or no clinical signs of allergy. The shots are specifically formulated for your cat based upon the information obtained from allergy testing. The process is not without difficulty and one should not expect hyposensitization to end all itchy skin concerns. Administration of allergy shots is a financial and time investment.

• Allergy shots may take 6 to 12 months to begin working
• 25% of atopic animals will not respond to allergy shots
• 25% of atopic animals will require steroids or antihistamines intermittently
• Allergy shots are administered by the owner
• Adverse anaphylactic responses are rarely observed with allergy shots.

Unfortunately, there is no cure for skin allergies and atopy may be a life-long problem. The only way to eliminate an allergy is to eliminate exposure to the source, which is often not possible. Most treatments aim to alleviate the symptoms associated with allergies. Coping with an itchy cat can be a very frustrating experience-we are here to help you keep your cat as comfortable as possible.

Websites about Atopic Dermatitis:

• veterinarypartner.com

Adapted from ‘Dermatology’ by Carol S. Foil and ‘Airborne Allergies’ by Wendy C. Brooks: Veterinary Information Network.

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