Canine Atopic Dermatitis
Multiple breeds have been shown to be predisposed to canine atopic dermatitis (AD), but the prevalence within a breed largely depends on the genetic pool and region. Breeds predisposed to development of AD include:
The age of onset is generally between 6 months and 3 years. There is no sex predisposition.
Clinical signs may be seasonal, nonseasonal, or nonseasonal with seasonal flares. Pruritus is the characteristic sign of AD. The feet, face, ears, flexural surfaces of the front legs, axillae, and abdomen are the most frequently affected areas, but lesion distribution can vary with the breed. Primary lesions are uncommon and consist of erythematous macules, patches, and small papules. Most lesions develop secondary to self-trauma and are due to the presence of secondary infections. they include alopecia, erythema, scaling, hemorrhagic crusts, excoriations, lichenification, and hyperpigmentation.
Secondary skin and ear infections with Staphylococcus and Malassezia spp are common and often worsen the clinical signs. Chronic or recurrent otitis may be the only complaint in a small number of animals.
Diagnosis of canine atopic dermatitis is challenging and is based on signalment, clinical signs, history, and the exclusion of other pruritic skin diseases (see differential diagnoses below), not on laboratory tests. Prospective studies have revealed the following clinical features compatible with a diagnosis of AD, known as Favrot's criteria:
The sensitivity and specificity of these set of diagnostic criteria are reported to be 85% and 79%, respectively. These criteria do not apply to cases of food-induced atopic dermatitis. Canine atopic dermatitis is very likely if at least five of the above criteria are present and other differential diagnoses have been ruled out.
Allergy testing (intradermal or serologic) is a diagnostic aid that measures increased levels of tissue-bound or circulating IgE; alone, it is not diagnostic but rather reflects exposure. The primary reason to pursue intradermal or serologic allergy testing is to identify the offending allergens in an individual animal and to formulate allergen-specific immunotherapy. Test results are significant only if the offending allergens identified are compatible with the history or seasonality of pruritus.
The most important differential diagnoses for pruritic skin conditions include:
Atopic dermatitis cannot be cured, but the disease can in most cases be managed to improve quality of life of patients and owners. Client education is important, because this is a lifelong disease that requires lifelong management and regular progress checks. Management options depend on the severity of the clinical signs and whether the pruritus is seasonal or year round.
Avoidance of allergens: This may be the best choice, but it is difficult, if not impossible, to do unless a specific allergen can be identified.
Relief from pruritus: By definition, this is a pruritic skin disease; itching may be relieved via antipruritic drugs alone while waiting for allergen-specific immunotherapy (ASIT) to be effective, or in combination with ASIT in partially responsive cases (see below).
Bathing: Bathing dogs with AD may decrease pruritus. Bathing can reduce allergen load and can be the most effective way to implement avoidance. Weekly to biweekly baths are recommended. In dogs with a history of flares due to microbial overgrowth, routine use of antimicrobial shampoos may help decrease the incidence of secondary infections. Matching the active ingredients with the most likely problem seen adds extra benefit: eg, in cases of superficial pyoderma, the use of an antibacterial product like chlorhexidine will likely give the best results.
Recognition and control of flare factors: A relapse of clinical signs in a dog that is otherwise well controlled should prompt an investigation into what caused the exacerbation of pruritus. Recognized flare factors include, but are not limited to, fleas, food and environmental allergens, and secondary infections such as Malassezia dermatitis, superficial pyoderma, and otitis. These need to be investigated and addressed, and the level of pruritus must be re-evaluated before choosing longterm antipruritic therapy.
In acute flares:
Select Therapeutic Agents for Atopic Dermatitis
Allergen-specific immunotherapy is the only treatment that can change a patient's immune response to allergens and induce remission of clinical signs. It remains the treatment of choice of most dermatologists and allergists. ASIT attempts to increase an animal’s tolerance to environmental allergens by inducing the development of anti-inflammatory cytokines, such as IL-10. IL-10 has been has been associated with production of IgG and decreased IgE levels. In people with AD, early administration of ASIT prevents progression of the disease.
ASIT consists of the administration of increasing doses of the offending allergens until a maintenance dose is reached. ASIT can be administered via injections or orally, which are equally effective; therefore, clients should choose a method based on the ease of administration.
For injectable ASIT, the interval between maintenance dosages varies with different protocols. Adjustments in the interval are based on the animal’s response and may vary from a few days to 3–4 weeks; for oral ASIT, the administration is once or twice a day. Owners are advised not to expect much response for 6 months and are asked to commit to at least 1 year of therapy before deciding the usefulness of immunotherapy. The best assessment of response is to compare the degree of disease or discomfort between similar seasons.
Side effects are uncommon; increased pruritus is the most commonly reported one. Most of these cases respond to premedication with an antihistamine, but some require dose adjustment. Less common side effects include pain at the injection site, urticaria, lethargy, and, very rarely, anaphylaxis. Owners should be asked to administer ASIT when able to monitor their animals for at least 30 minutes after administration. Owner education is very important when initiating ASIT. The need to perform the treatment for at least 12 months before evaluating the response, the best route of administration, the protocol, and the rate of success should be discussed in detail. The success rate of ASIT is approximately 66%, and some patients may require additional therapies such as regular bathing, essential fatty acids, and antihistamines.
Atopic dermatitis is a genetically predisposed chronic inflammatory and pruritic allergic skin disease with characteristic clinical features.
Diagnosis is based on clinical signs, history, and exclusion of other causes of pruritis.
Management includes medications and baths that relieve pruritis and avoidance of allergens.
Client education and monitoring are key for treatment success.
Olivry T, deBoer DJ, Favrot C, et al. Treatment of canine atopic dermatitis: 2015 updated guidelines from the International Committee on Allergic Diseases of Animals (ICADA), BMC Veterinary Research, 2015, 11:210.
Also see pet health content regarding dermatitis and dermatologic problems in dogs.