Atopic Dermatitis in Cats

Atopy is a type I hypersensitivity reaction that causes itching in cats. It is associated with the presence of skin-fixed or circulating immunoglobulin E (IgE) that is specific to environmental allergies. Feline atopy has also been called non-flea, non-food allergic dermatitis.

Atopy is caused by an allergy to airborne substances in the environment, either by absorption through the respiratory tract or contact with the skin. It is thought to be an inherited disease, and is the second most common type of dermatitis in cats, following flea allergy dermatitis. Atopic dermatitis has also been documented in humans and dogs. Allergens that trigger this disease can be both indoor and outdoor, and seasonality can provoke clinical signs based on the inciting allergen and exposure.

Symptoms of atopy usually begin relatively early in life, often by one year of age. They’re usually 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 and more specific to certain substances. Eventually, their itchiness can occur year-round.

Symptoms of Atopic Dermatitis

Cats that suffer from atopic dermatitis tend to be pruritic (itchy) and will often over-groom their hair coat, legs, and paws. Their skin may be red and irritated due to scratching and self trauma.

Clinical signs of atopic dermatitis are very similar to other forms of dermatitis in cats. Miliary dermatitis is a term that describes the pattern of lesions that some cats get with atopic dermatitis. This pattern isn’t seen in dogs or humans with atopy. Miliary dermatitis can also be seen with flea and food allergies, since they’re a manifestation of allergies in cats, as opposed to being a distinct form of atopy.

Clinical signs include:

• Chewing at the paws
• Scratching or rubbing of the face on the ground or with the paws
• Scratching of the ears
• Shaking the head
• Over-grooming

Diagnosis of Feline Atopic Dermatitis

Atopic dermatitis looks similar to other types of dermatitis (like mange, ringworm, and pemphigus foliaceus), therefore, your veterinarian will need to examine your pet, rule out other diseases, and isolate the diagnosis.

Diagnosis of atopic dermatitis often includes:

• A complete medical history, which helps to isolate a pattern or seasonality (if present).
• Thorough physical examination, including checking the ears and the skin of the face and paws. Occasionally, redness between the toes or around the muzzle of the face are the only presented symptoms.
• Skin scrapings to eliminate other diagnoses, such as demodectic or sarcoptic mange (caused by mites). 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.
• Fungal culture to rule out ringworm (also called dermatophytosis). Dermatophyte infections of the skin can mimic many other skin diseases, and a fungal culture is typically part of the diagnostic process.
• Skin culture to rule out a secondary bacterial infection, like pyoderma.
• A food trial may be recommended to rule out food allergy. This typically entails your pet being fed a new food as its only source of nourishment for 6 to 12 weeks. If the symptoms don’t improve, food allergy is excluded as a diagnostic possibility.
• Allergy testing, if no other measures can pinpoint the cause. Intradermal allergy testing (skin testing) is done to determine which allergens caused the skin reaction. Hair is clipped from one side of the chest and small amounts of a variety of allergens are injected into the skin. Light sedation may be necessary to allow proper restraint during the procedure.
  • Intradermal skin tests are considered the gold standard for allergy testing in cats. This is done through a veterinary dermatologist and helps to determine specific allergens that are causing the hypersensitivity reaction.
  • Serology testing is also available, but is less reliable. This is a blood test that detects allergen specific IgE.
  • On occasion, a dermatologist will use a combination of both intradermal and blood allergy testing to help isolate particular allergies in cats.
  • Saliva testing for allergens is the least reliable method for allergy testing.

Treatment of Feline Atopy

Two primary forms of treatment for atopy are drug treatment and immunotherapy. The ideal treatment for most moderately and severely-affected animals is some combination of both types.

Drug therapy relieves the symptoms of atopy, but does not treat the underlying allergy itself. Most cats with atopy are young, and may require years of therapy.

Drug treatments for atopy include:

• Antihistamines are less effective for cats than they are in humans, working on only 25 to 30% of feline patients. They are often tried first because they have fewer adverse effects than 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 for your cat.
• Fatty acid supplements may relieve itchiness (i.e., pruritus) by modulating the immune response. Certain fatty acids such as eicosapentaenoic acid (found in fish oil) help change the chemical composition of cell membranes and the types of chemical mediators (i.e., prostaglandins) produced during the allergic reaction, 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.
• Antibiotics may be needed to treat pyoderma or yeast infections, since secondary bacterial infections are common in cats with allergic skin disease.
• 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.
• When the above treatments are no longer effective, corticosteroids, such as prednisolone, 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 that are on long-term corticosteroid medications are at a higher risk to develop diabetes mellitus or exacerbate cardiac issues (like heart disease).

Immunotherapy

Immunotherapy (like hyposensitization, desensitization, and allergy shots) 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 to allergens through the immune system. This technique is effective in 60 to 80% of atopic cats.

Initially, an extract of the allergens selected by allergy testing is prepared. A small amount is injected every 1 to 2 days, with the dosage gradually increasing. Due to the frequency of injections, your veterinarian 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.

Home Care

Atopy is incurable 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. 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 pruritic skin diseases, such as flea allergy dermatitis, may have an additive effect on your cat’s skin condition. Year-round topical flea and tick preventative medication is imperative for all cats (even indoor-only pets).

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.

Follow-Up Care for Cats with Atopy

Atopy varies considerably in intensity based on the individual animal and its environment. Therefore, home monitoring and close communication with your veterinarian are vital for success. Treatment is effective if individualized to the patient.

Follow-up for atopy may include the following:

• Proper administration of 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.
• Observe cats on immunotherapy for signs of increased itchiness, 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 are extremely rare. Also, remember to have patience with immunotherapy. It should be tried for 9 to 12 months before concluding that it was a failure.
• Shorten the interval between injections, if your cat begins to scratch before the next injection is due and you receive approval from your veterinarian. Keep a log of how much extract was given and record the date of the injections, since schedules may become complicated.
• 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 happen while waiting for generalized improvement and will need to be treated appropriately.
• Install in-home air filters to help keep dust mites and offending allergens away from your cat.

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

In-Depth Information on Diseases that Mimic Atopy

Itching is a symptom in many feline skin diseases, which may lead you to believe that your cat suffers from atopy. Ruling out other causes of pruritus is an important part of establishing a diagnosis.

Diseases that mimic atopy in appearance include:

• Food allergies. Cats with food allergies often chew their feet, rub their faces, and scratch their ears. Thus, the symptoms of food allergies 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 occur at any age. A cat that has an onset of signs, but 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, and only about 50% of affected cats will respond. During the initial stages of diagnosing feline dermatitis, diet trials may be recommended to isolate food allergies if present.
• Flea allergy dermatitis. This is the most common allergic skin disease seen in the United States. Like food allergies, it is variably responsive to corticosteroids. Cats with flea allergies tend to chew and scratch at their back ends, creating lesions over the rump, on the neck, on the belly, and between the hind legs. This behavior helps to differentiate this disease from atopy. However, it is possible to see atopy and flea allergies in the same animal.
• Scabies. This itchy skin disease is caused by the sarcoptic mange mite. Affected cats are extremely itchy and often have lesions on their ears, elbows, and hocks. 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, ultimately leading to infection. Some animals with atopy are only mildly itchy most of the time, but it may be much worse when they also suffer from pyoderma.

Concerned about vet costs related to allergies? Pet insurance may be able to help. Click here to learn more.