Atopic dermatitis is a predisposition to become allergic to normally innocuous substances, such as pollen, housedust and dust mites, and other environmental allergens.
CAUSE Although an inherited predisposition exists the exact mode of inheritance has not been established.
Susceptible patients become sensitized to various allergens during an initial exposure. Subsequent re-exposure by inhaled and percutaneous (absorbed through the skin) routes then provokes an inflammatory reaction. Itching leads to scratching and licking, which leads to skin irritation, which leads to more itching...
Secondary bacterial and yeast infections can then complicate the problem.
PATIENTS AND COMMON HISTORIES The incidence of atopic dermatitis has been estimated at 3 to 15% of the dog population; unknown but smaller incidence in cats. In our experience, the incidence in our canine patients is greater than 10%.
It can occur in any breed, but because of inherited factors we see it more commonly in certain breeds and families. West Highland white terriers and golden retrievers are the most commonly affected breeds seen at YVC.
Signs usually appear between 1 and 3 years of age, and range in onset from 3 months to 6 years. In the first year they may be so mild that they are not noticed, but they are usually progressive and apparent before 3 years.
Males and females are equally affected.
SIGNS Itchiness is the primary sign, and the face, feet, and the areas under the tail and behind the front legs are the most common body regions affected. Lesions vary from none to: broken hairs, salivary discoloration of the fur, redness, papules (tiny bumps), crusts, hair loss, increased skin pigmentation, excessively oily or dry skin, thickened skin, and sweating.
Secondary bacteral and yeast infections and chronic ear infections are common. Conjunctivitis may also occur, either as a primary allergy sign or secondary to inflammation of the eyelids.
Our atopic feline patients often have miliary dermatitis (little bumps over large areas of their bodies), hair loss from excessive grooming, facial scabs, ear infections, and occasionally thick red sores on the skin or in the mouth called eosinophilic plaques.
SIMILAR PROBLEMS Some other common problems can be mistaken for atopic dermatitis. Food allergy, flea allergy, sarcoptic mange, bacterial skin and yeast infections, and contact allergy can have very similar signs.
DIAGNOSIS The pet's history and physical exam can give us a strong presumptive diagnosis.
If a pet has at least three of the the criteria from each of the following major and minot categories, then it is likely that pet has atopy:
Major criteria: itchiness, face and feet affected, chronic or relapsing skin inflammation, breed predispostion and/or family history
Minor criteria: onset of signs at less than 3 years old, conjunctivitis, facial redness, bacterial skin infection, excessive sweating, positive skin test reactions, and elevated allergen-specific blood tests
Further diagnostic testing is sometimes worthwhile. We feel skin biopsy is a very valuable test to help us rule out other problems, and characterize the type and degree of skin problems. Skin testing and blood testing are available, but, in our practice experience, no commonly worthwhile.
MANAGEMENT SCHEDULE Persistent monitoring of itch, self-trauma, and skin infections is necessary. We recommend re-examining our atopic patients once every 2 to 8 weeks whenever a new course of therapy is started. Once an acceptable level of control is achieved, we re-examine every 3 to 12 months. For patients on chronic cortisone therapy, an exam, blood profile and urinalysis once every 6 to 12 months is advisable.
TREATMENT OPTIONS We tailor our treatment recommendations for each atopic pet. Briefly, treatment options include:
TOPICALS Shampoos, sprays, rinses, and spot-ons can have soothing and antiitch effects, and can also help by removing the dust, pollen and dander from the pet's skin.
IMMUNOTHERAPY (ALLERGY INJECTIONS) Some veterinary dermatologists report high success rates for treatment with desensitizing injections. We feel that they are usually not practically worthwhile: the program is expensive, it requires the owner to give daily injections and commit to regular testing to monitor and adjust therapy, and it is not without significant side effects.
CORTISONE Cortisone is the cornerstone of atopy treatment. It is very safe to use in the short-run, to break the itch/scratch vicious cycle, and in the long run to keep the pet comfortable. We use tablets for dogs and injections for cats.
ANTIHISTAMINES It would be nice if antihistamines worked as well for allergic dogs and cats as they do for allergic people, but they unfortunately do not. They can, however, work synergistically with other treatments, reducing the need for these other treatments. In order to determine if antihistamines will work for a particular patient we have to do 1 to 2 week trials with each of several antihistamines.
ALTERNATIVE DRUGS AND SUPPLEMENTS We think most atopic patients should take a fish oil (omega 3, fatty acid) supplement. A note of caution: many pets foods now advertise fatty acids in their ingredients and it is true with most of them that there are some fatty acids in them, but rarely is there enough fatty acid in food to be considered therapeutic. If you would like to use fatty acids the you should administer one in addition to the food, or consult with us about the food.
Tricyclic antidepressant medications sometimes work to control the itch of atopy for dogs.
Cyclosporin is an immune system suppressant that can be used alone or along with other treatments. Because it is costly, does not always work, and has it's own side effects, we usually do not use it unless most other treatments fail.
CONTROL OF SECONDARY AND SIMULTANEOUS PROBLEMS Secondary problems, including ear inflammation and bacterial and yeast infections need to be treated. Controlling skin problems that can occur simultaneously with atopy, including fleas, mites, and food allergy, will subsequently make the atopy more manageable.
PROGNOSIS Atopy is a very frustrating disease because it is progressive and cannot be cured. Successful management often requires lifelong therapy and occasional adjustments of treatment. That said, we have found that most pet owners are more than willing and able to provide the necessary care to keep their pets comfortable and happy.