Atopy

What is Atopic Dermatitis?

Atopic dermatitis (Atopy, allergic dermatitis) is an inflammatory and pruritic (itchy) skin disease, resulting from a hypersensitivity or over-reaction to a variety of commonplace substances in the environment. It is the second most common type of allergy (the first being Flea Allergy Dermatitis) in dogs.

It was once thought to be caused by inhaled allergens to which the dog’s immune system overreacts, however, although the specific mechanism of atopy is still unknown, it is now thought to be due to contact of the allergic particles directly on the skin. Breaks in the skin barrier (epidermal barrier) are thought to facilitate the contact of allergens with the bodies immune cells. The resulting exaggerated immune response leads to the symptoms of inflammation and itch.

Most atopic dogs will start showing symptoms between the ages of 6 months and 3 years. There is a strong genetic tendency in dogs, with Golden Retrievers, Labradors, Terriers, Dalmatians and Shar-peis among the predisposed breeds. In Australia, German Shepherds, Rottweilers, Bull Terriers, West Highland White Terriers and Boxers are predisposed.

What sort of things cause it?

There are a whole variety of allergens which can produce atopy. These are very similar to some of the things causing hay fever or human asthma.

When the affected individual is exposed to dust, pollens, moulds or dust mite, for example, an allergic response can occur.

What happens to the dog when this occurs?

Atopy in the dog is usually seen as severe generalised itching. The dog chews, licks, scratches or rubs themselves. Saliva may stain light coloured hairs so that dogs that lick their feet excessively will have orange or reddish brown hair. The dog may also scratch and rub the face, particularly around the eyes and ears. The axillae (armpits), groin and the inside of the thighs may also be affected. They may have recurrent ear infections. Occasionally, there may also be respiratory signs like a person with hayfever, such as sneezing and conjunctivitis.

How do you diagnose this condition?

Diagnosis is not easy. Other skin diseases can mimic atopic dermatitis or be superimposed on it. Diagnosis is therefore based on the presence of the signs discussed above and ruling out other causes of pruritis, e.g. other allergies such as fleas or infections such as a yeast.

Careful history taking will narrow down the causes. For example, if it only occurs in the spring when certain pollen is prevalent this narrows the field of investigation.

Treatment options

Treatment will need to be tailored to the individual pet however it will generally involve three factors:

1.   Controlling the allergy

Intradermal allergy testing (skin tests) and/or serology tests (blood tests) can be performed to identify the specific environmental allergens in dogs with atopic dermatitis. These can then be used as the basis of a treatment called allergen-specific immunotherapy. This treatment involves a series of ‘allergy shots’ or sometimes oral liquid which is given in gradually increasing concentrations in an effort to make the allergic reaction less sever. Such testing and treatment can be complex and may require referral to a dermatologist.

Medications such as prednisolone, cyclosporin and the newer oclacitinib can be used to modify and suppress the dog’s immune response. This results in less inflammation and itching. Your vet will discuss the costs and possible side effects of these medications.

2. Improving the skin barrier function

In atopic animals, the normal protective layer of the skin is damaged, allowing increased penetration of allergens and stimulation of the immune system. Skin function can be improved with oral supplementations of essential fatty acids as well as the use of various shampoos, conditioners and bath oils. Frequent bathing in an appropriate shampoo can provide a direct soothing effect to the skin, help with improved skin hydration and facilitate the physical removal of surface allergens.

3. Controlling secondary infections

It is very common for atopic dogs to get secondary bacterial and yeast infections which can worsen the symptoms. These must be identified and treated.

My dog only seems to itch in the spring and I have been told she has a seasonal allergy.  What does this mean?

Probably she is allergic to a particular type of pollen that is only produced during a specific period of the year, e.g. in spring.  Some atopic dogs will have an all year problem, in other words it is not seasonal. This means the allergen is present throughout the year. With some dogs the cause is often house dust mites.

Another explanation may be that the dog has developed separate hypersensitivities to so many different allergens that at least one is present at any one time.

My dog has a grass allergy each year. Does that mean it should not walk on grass?

No. So-called grass allergies are more correctly grass pollen allergies. Closely cut grass with no seeding heads will not cause problems. However, do remember the pollen is airborne and cutting your own grass will have little effect if you live next door to a flowering meadow.