Atopic Dermatitis
by
Christopher Schwarz, DVM
Atopic dermatitis is the most common presentation of allergies in dogs. Atopic dermatitis is a form of environmental allergy where the clinical signs are expressed by skin changes, including itching, seborrhea, scaling, hair loss, and secondary yeast and bacterial infections. A study performed at CSU showed that 90% of the cases of allergies seen in Colorado are atopic dermatitis cases, with most of the remaining cases being food allergies (fortunately there are not many fleas in Colorado reducing the cases of flea allergy dermatitis significantly here).
Atopic dermatitis differs from atopy in Humans significantly. Most cases of atopy in humans occur at a younger age with people often times outgrowing their allergies. Dogs tend to have occurrence early in life, with the progression worsening with age until they plateau at a very itchy level. The itching is due to environmental allergens in both cases (pollens, grasses, mold spores, dust mites, dander, etc.) and can be worse seasonally or can be bad year-round based on the cause of the allergy.
It has been found that Atopic Dermatitis in dogs leads to the destruction of the top-most layer of skin. This layer not only produces oils that help protect the skin, but also helps cover the nerve endings. As the disease progresses, the nerves become more exposed to the allergens, leading to worsening itching leading to worsening damage. Topical therapy should be extremely beneficial because of this, however in practice unfortunately topical therapy has not proved to work well.
Atopic Dermatitis has been by many to be considered the most difficult and frustrating diseases to treat. The primary goal of treatment is to lessen the clinical signs to a point where everyone in the house is happy. There are three ways to obtain this goal.
The first option is to try to “Cure” the disease. This is done with allergy testing and desensitization. Allergy testing can be done with a blood test (typically done through general practitioners) or intradermal testing (done by dermatology specialists). After testing is done to determine what the pet is allergic to, then desensitization with a gradually increasing exposure to the allergens over 12 months is done. This method has approximately a 50% success rate (half of the dogs continue with the treatment, half do not).
The second option is avoidance of allergens. Allergy testing is done to find out what we are allergic to, and then they avoid all of those things. Unfortunately this is tougher than it sounds as the air around us is not sterile, and there are only extremely rare success stories out there.
The last option is to treat the clinical signs. This has been the primary source of treatment, with topical therapies/bathing and antihistamines having the lowest success rates (~10-30%) and Corticosteroids having the highest success rate (>95%). Due to the side effects of steroids, several other medications have been developed, including Apoquel, Atopica, and Cytopoint. These medications all have their potential issues and concerns, however they have helped to keep so many pets comfortable without the side-effects of long-term corticosteroids.
This disease, because of its chronic nature and often inadequate response to therapy, combined with the sadness of seeing your pet being so uncomfortable, is by and far one of every veterinarians most hated diseases. Other diseases, ranging from fleas, lice, mange, certain skin cancers, autoimmune diseases, food allergies, and other infections can look exactly the same as well. This makes a diagnosis difficult and frustrating as well. Patience and education is the best way to help work our way through a diagnosis of atopic dermatitis.