Dogs with Atopic Dermatitis: Causes, Diagnosis, and Treatment

Atopic dermatitis is a disease in which there is an inherited tendency to develop IgE antibodies in response to exposure to allergens that areinhaled or absorbed through the skin. This extremely common allergic skin disease is second only to flea allergy dermatitis in frequency, and affects about 10 percent of dogs.

Atopy begins in dogs 1 to 3 years of age. Susceptible breeds include Golden Retrievers, Labrador Retrievers, Lhasa Apsos, Wire Fox Terriers, West Highland White Terriers, Dalmatians, Poodles, English Setters, Irish Setters, Boxers, and Bulldogs, among others, although any dog may be affected. Even mixed breeds may suffer from atopy.

Signs generally first appear at the same time as the weed pollens of late summer and fall. Later, other pollens begin to influence the picture: tree pollens in March and April; then grass pollens in May, June, and early July. Finally, the dog starts to react to wool, house dust, molds, feathers, plant fibers, and so forth. With prolonged exposure and multiple allergens, the condition becomes a year-round affair. Some dogs have indoor allergies (usually house dust, grain, mites, or molds), so they may react all year-round from the start.

In early canine atopy, itching is seasonal and the skin looks normal. Dogs scratch at the ears and undersides of the body. The itching is often accompanied by face-rubbing, sneezing, a runny nose (known as allergic rhinitis),watery eyes, and licking at the paws (which leaves characteristic brown stains on the feet). In many dogs the disease does not progress beyond this stage.

When it does progress, an itch-scratch-itch cycle develops with deep scratches (called excoriations)in the skin, hair loss, scabs, crusts, and secondary bacterial skin infection. These dogs are miserable. In time, the skin becomes thick and darkly pigmented. A secondary dry or greasy seborrhea with flaky skin often develops in conjunction with the skin infection.

Ear canal infections may accompany these signs, or may be the sole manifestation of atopy. The ear flaps are red and inflamed, and the canals are filled with a brown wax that eventually causes bacterial or yeast otitis.

Canine atopy, especially when complicated by pyoderma, can be difficult to distinguish from flea allergy dermatitis, scabies, demodectic mange, food allergies, and other skin diseases. The diagnosis can be suspected based on the history, location of skin lesions, and seasonal pattern of occurrence. Skin scrapings, bacterial and fungal cultures, skin biopsy, and a trial hypoallergenic test diet should be considered before embarking on an involved course of treatment for atopy. It is important to treat and eliminate fleas. The majority of dogs with canine atopy are allergic to fleas and may have an associated flea allergy dermatitis complicating the picture.

Treatment: The most effective long-term solution is to change the dog's living circumstances to avoid the allergen. The atopic dog is usually allergic to many different allergens, however, and often it is not possible to avoid exposure to them all.

Most dogs with atopy respond well to treatment. A first and most important step is to reduce the threshold for scratching by treating and eliminating all associated irritative skin problems, such as fleas, seborrhea, and pyoderma. Wipe the dog down with a damp towel when she comes in from outdoors, which helps remove pollens picked up in the coat.

Antihistamines control itching and scratching in 20 to 40 percent of atopic dogs. Corticosteroids are the most effective anti-itch drugs, but also have the most serious side effects. They are best used intermittently in low doses and for a limited time. Preparations containing hydrocortisone withPramoxine are often prescribed for treating local areas of itching. Pramoxine is a topical anesthetic that provides temporary relief from pain and itching.

Derm Caps and other essential omega-3 fatty acid products derived from fish oils have produced good results in some dogs. They are used as nutritional supplements in conjunction with other therapies. A variety of shampoos is available and may be prescribed by your veterinarian to rehydrate the skin, treat bacterial infection, and control seborrhea.

Dogs who do not respond to medical treatment can be considered for immunotherapy with hyposensitization. This involves skin testing to identify the allergen(s) and then desensitizing the dog to the specific irritants through a series of injections given over a period of 9 to 12 months or longer. Some dogs will require periodic boosters during times when allergens are heavy.

Some dogs with atopy benefit from switching to a higher-quality dog food, even if they don't have a food allergy. And if they are allergic to house dust mites, they often cross-react with grain mites and will benefit from a canned food or kibble that has no grain.

This article is excerpted from “Dog Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.