In the first of 2 articles on atopic dermatitis in dogs and cats, dermatology expert Anita Patel explains what the condition is, what it means for your pet, and how it can be diagnosed.
What is atopic dermatitis?
Many of you will have been told by your vet that your pet has atopic dermatitis, but what is it? Atopic dermatitis is the visible sign of a hypersensitivity (allergic) reaction; specifically a reaction to something (called an allergen) in your pet’s environment, either indoors or outdoors. It may be a reaction to pollens, or moulds, or to mites, such as house-dust mites.To complicate the issue further, some pets can have an allergic reaction to some foods, which is ‘food induced atopic dermatitis’.
There are a variety of allergens in an atopic animal’s environment which may trigger an allergic reaction
Hypersensitivity is when the immune system goes into an overdrive. Normally when a pet is exposed to an allergen, its immune system produces antibodies to the allergen and once it has performed its protective role it will automatically revert to normal; however, if your pet is predisposed to atopic dermatitis its immune system continues to produce antibodies, which may then result in a hypersensitivity.
What are the main signs of atopic dermatitis in dogs and cats?
The hallmark of atopic dermatitis is an itch, usually without any visible signs other than a reddening of the skin. Often when I ask an owner where their pet animal is itching they say “Oh, Fido does not scratch”, but dogs exhibit itch by licking, rubbing, or chewing at the itch as well as by scratching at it.
The itching usually starts between the ages of 6 months and 3 years. Initially it may be seasonal – that is it occurs only at certain times of the year – but over the years that can change. Spring and summer time itching is usually associated with pollen allergies (e.g. tree, grass and weed pollens) whereas winter or all year round itching is associated with indoor allergens such as house dust and storage mites or mould allergens. Food associated atopic dermatitis is likely to be non-seasonal, unless your pet is only being fed the food intermittently (e.g. on holiday). The itchy areas of the skin are usually the face, ears, feet and underside.
This photograph shows changes on the belly of a golden retriever with atopic dermatitis
Often the condition is complicated with secondary infections (bacterial and/or yeast) and sometimes, just to complicate the situation further; some patients have been known to develop an allergy to the infection as well. Infections increase the level of itching and so just treating these will often decrease or stop the itch entirely. Once infections occur a rash may appear on the belly, neck and feet and your pet will lick, chew or scratch these areas. Infected skin is malodorous (has a bad smell) and, as the infection progresses the skin becomes thickened, blackened and crusty. If your pet then licks or scratches these areas aggressively, the skin can become broken or ulcerated, and also bleed.
Since similar lesions can also be seen with parasitic infestations (e.g. mange) these must be ruled out, or treated, at the same time as the allergy.
Recurrent ear infections are also associated with food or environment associated atopic disease. Usually the ear flap and the ear canals appear red in the early stage, which is then often followed by head shaking, discharge and swelling.
What is my pet allergic to?
To find out what your pet is allergic to, your vet can perform an allergy test, which will either involve sending a blood sample to a laboratory, or performing an intradermal skin test. Both forms of testing have their advantages and disadvantages. The results of the test should be interpreted bearing in mind the seasonality of the condition and your pet’s environment.
This photograph shows an intradermal skin test which has been performed on a dog. Very small amounts of allergens are injected under the skin to identify which ones that particular animal is allergic to by provoking a small, controlled allergic response.
Allergy testing identifies the allergens to which your pet might be allergic to, but the main reasons for testing should be to find out what your pet is allergic to, so as to be able to improve quality of his/her life. Your vet can use the information for therapeutic purposes and to look at means of reducing the allergen load in the environment. The lower the allergen load, the lesser the itch and the easier it will be to keep your pet comfortable. One can compare atopic dermatitis in dogs to hay fever in people. If you have hay fever and you stand in a field full of flowers whose pollen you are allergic to, you will suffer severely, as opposed to if you stayed indoors when the pollen count is high. The same goes for dogs, by reducing the allergen load you will be helping to relieve your pet’s symptoms.
In the next article, Anita will discuss how atopic dermatitis in dogs and cats can be managed.