Dog: Atopic Dermatitis

Other common/scientific names: atopy, allergic dermatitis, allergic inhalant dermatitis

An allergy is an abnormal reaction of the body to an allergen which is a substance that triggers the allergic reaction. An allergic reaction is a hypersensitivity response occurring when the body’s immune system overreacts to the substance. Unlike people, dogs rarely have respiratory allergies but instead exhibit allergic symptoms as skin conditions.

Dogs develop atopic dermatitis as a result of an allergic reaction to common environmental substances such as molds, dust mites and pollens. These allergens can be inhaled, swallowed or acquired by direct contact. Since repeated exposure to the allergens is necessary to cause atopic dermatitis, this condition is usually first seen in dogs one to three years of age. It is thought to be inherited and commonly seen in Labrador Retrievers, Terriers, Cocker Spaniels, Dalmations and Lhasa Apsos. Another component of atopic dermatitis is food allergies where a dog develops an allergic type reaction to certain foods they ingest. Food allergies will be discussed in a separate article.

Itching

Dogs with atopy will usually lick, chew, bite or scratch at their feet, muzzle and axillary (armpits). As the dermatitis progresses, the entire body may be affected. Other signs include hair loss and red, inflamed skin from self-trauma due to scratching. Depending on the particular allergen, these symptoms may be mild and seasonal (e.g. pollens). Over time, these signs tend to become more severe and continue for a longer period of time. Dogs can develop a secondary infection due to bacteria (Pyoderma) or yeast (Malassezia) resulting in raised papules, pustules and scabbing which further worsens the pruritis (itching). In chronic cases, the skin may become thickened, pigmented and develop a foul odor.

Dogs with atopic dermatitis may also suffer from flea allergy dermatitis. Because of this, it is important that any itching dog be carefully examined for signs of flea infestation. A skin scraping should also be performed on any itching dog to rule out ectoparasites such as sarcoptic mange, demodicosis and cheyletiellosis.

Allergy testing in the form of intradermal skin testing or serum allergen testing can be performed. With the intradermal skin testing, different allergens are injected underneath the skin. These areas are then observed for hypersensitivity to the allergen. With serum allergen testing, a blood sample is submitted to a laboratory and specific immunoglobulins are measured. The results from allergy testing can aid in the diagnosis of not only atopic dermatitis but also flea allergy dermatitis.

Successful treatment of allergies involves a multimodal approach. This includes:

• Systemic Therapy. These medications include oral and injectable antihistamines, corticosteroid anti-inflammatories and immunosuppressives. Omega-3 fatty acid supplementation is also thought to help with allergic dermatitis. Initially, a combination of these medications may be necessary to manage the pruritis. Systemic treatment can be successful in mild cases of seasonal allergy. Concurrent antibiotic or antifungal therapy may be needed to treat seconday skin infections.
• Hypo-sensitization Therapy. This treatment uses an allergy vaccine made specifically for the individual dog based on either intradermal skin testing or serum allergen testing. These injections are given daily for a period of time to desensitize your dog to the allergens. Once symptoms are controlled, theses injections are tapered to every other week or monthly. Hypo-sensitization is most successful in controlling severe atopic dermatitis.
• Topical Therapy. Topical remedies in the form of soothing and antipruritic shampoos and rinses are often used in combination with other therapies.
• Management of Allergens. While eliminating allergens from your pet’s environment may not be practical, reducing exposure to pollen can be accomplished by using air-conditioners, avoiding the outdoors in early morning and later afternoon and wiping down your dog with moist cloths after going outside.

Atopic dermatitis cannot be cured. Owners with affected dogs should be committed to lifelong management. While allergies can be chronic and frustrating, these dogs can live a healthy, symptom free life with proper treatment.

Many dogs with atopic dermatitis are also allergic to fleas and certain food stuffs. These dogs are much more sensitive to even a small increase in the amount of allergen. The allergic threshold is the amount or level of allergens at which a dog will show clinical signs of allergies. The lower the allergic threshold, the more sensitive the dog. It is extremely difficult to eliminate all the allergens in a dog’s environment. However, in order to provide relief for your dog, you do not need to eliminate them all. Rather, you only need to prevent the allergens from exceeding threshold. Because fleas are preventable, it is important to prevent a flea infestation in a dog with atopic dermatitis.

Abb. GGTEZS6V: A diagram illustrating the allergic threshold principle.

Molds, dust and pollen cannot be completely eliminated. However, diet control and regular treatment for ectoparasites can greatly reduce itching.