Managing canine atopy: It's all about strategy

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Atopic dermatitis affects an estimated 10% to 15% of the canine population, with some breeds more heavily represented than others. According to Darin Dell, DVM, DACVD, associate medical director at Wheat Ridge Animal Hospital in Wheat Ridge, Colorado, successfully managing atopy involves more than just knowing about the latest drugs.

“It's great to talk about treatment options, but the strategy is how we use all those things together,” says Dr. Dell, who is speaking today at the Fetch dvm360 conference in San Diego. In case you can't get to the session in person, here's his game plan for managing this condition.

Dr. Dell describes atopy as a genetic predisposition to overreact immunologically to allergens in the environment. Prevalence may be higher than estimated, he says. Some breeds, like bulldogs, likely have an even higher incidence because a skin change that may be considered “normal” for that breed could potentially be an allergy-related dermatologic abnormality, Dr. Dell explains.1

The first hurdle: Diagnosis

Atopy is considered a diagnosis of exclusion. When faced with a possibly allergic dog, a veterinarian needs to determine whether the problem is caused by or complicated by infection or another condition, such as hypothyroidism, which requires a different treatment.

“In a study I conducted, we looked at allergic dogs five and 10 years after diagnosis and found that owners considered antibiotics to be just as successful in reducing itching as steroids in 60% of patients,”2 Dr. Dell says. “Translation: Infection plays a role in the allergic, itchy dog much of the time. So, if your treatment isn't working, there's a good chance that undetected infection is a factor.”

Some veterinarians rely on allergy testing to diagnose atopy, but allergy testing is most helpful when used and interpreted in the proper context. “Allergy testing isn't a tool to diagnose allergies, because dogs that don't have disease signs can have positive results. Instead, we use this test to define the allergy and formulate immunotherapy,” Dr. Dell says, adding that a positive result doesn't prove that atopy is causing a patient's skin issues.

Allergy testing options include serum testing, which veterinarians can conduct in their office, and intradermal allergy testing, which is performed by a dermatologist. Serum allergy testing is convenient because it's a simple blood test, but it has limitations. For example, these tests measure the patient's immunoglobulin E (IgE), but some atopic dogs don't produce large amounts of IgE, so even if they're symptomatic, the test may be negative. Also, serum allergy test results vary seasonally, which can affect test accuracy.

Dr. Dell cautions that allergy test results can also vary among laboratories. He cites a study in which serum from 10 allergic dogs was sent to four different laboratories, with poor agreement among the results. “The agreement among the four assays was only slightly better than what would be expected due to chance,” he says.3

Intradermal skin testing has the advantage of accuracy. However, drawbacks include limited access, required withdrawal times for some glucocorticoids and the need to sedate and shave patients for the procedure.

What if your magic pill doesn't work?

If your intended therapy isn't working, here are some troubleshooting tips Dr. Dell provides to get your patient back on track:

1. Recheck. Not only do rechecks offer an opportunity to re-examine skin lesions and follow up with the client, but they also give you a chance to investigate new problems (such as hypothyroidism) that can contribute to the condition.

2. Rule out infection. Check for bacteria, yeast, mites and dermatophytes.

3. Gather more information. Clarify the medical history and clinical signs with the client, determine whether at-home treatment is being implemented properly and reiterate what the client should expect with therapy.

4. Decide whether to change your core therapy. Also determine whether supportive therapies (such as antihistamines or shampoo) may be helpful.

Implementing your treatment strategy and managing expectations

In terms of drug categories, veterinarians have several options for managing atopic dermatitis in dogs:

Steroids have traditionally played a major role in managing atopy, but veterinarians wary of potential side effects may try antihistamines. “It's not wrong to use antihistamines, but by the time a dog gets to me, antihistamines are not usually very helpful anymore,” Dr. Dell says. “They may work initially, but be aware that allergies worsen over time, so antihistamines may not work forever.”

“Immunotherapy modulates the immune response instead of suppressing the allergic signs. It can also help prevent new allergies from developing,” Dr. Dell says. Additionally, immunotherapy can stop a patient's allergies from worsening over time (which occurs frequently), and it's the only actual cure for atopy, he added. Immunotherapy is available by injection as well as sublingual drops, although the drops must be given more frequently. Immunotherapy is considered 70% successful, but some dogs need concurrent treatments to keep clinical signs under control. It's also important to inform owners that a positive response can take 12 months, so a long-term commitment is required, Dr. Dell says.

Cyclosporine (Atopica-Elanco) works well as long as you understand a few things about it, Dr. Dell says. It may take four to six weeks to work, so some dogs need concurrent therapy initially. Cyclosporine may not be ideal if you need fast results, but it may be a good choice if a patient has a more chronic issue, such as interdigital cysts or pododermatitis. Vomiting and diarrhea are the most common adverse effects with cyclosporine, but Dr. Dell says he rarely needs to stop the medication. Reducing or dividing the dose, giving the medication with food or freezing the pills before administration can reduce vomiting. Gingival hyperplasia is another potential adverse effect. “If you see this effect but the drug is working well for the dog's allergy, I recommend lowering the dose instead of stopping the drug completely,” Dr. Dell said.

Oclacitinib (Apoquel-Zoetis) usually works quickly, which is an important advantage of this therapy. It works by blocking interleukin-31 (IL-31) at the Janus kinase (JAK) pathway. Because IL-31 is an important chemical mediator of itching, blocking this cytokine provides effective relief. Oclacitinib also blocks other mediators involved in allergy, such as IL-2 and IL-6.

Cytopoint (canine atopic dermatitis immunotherapeutic-Zoetis) is a more recent addition to the arsenal of atopy therapies. Cytopoint is a monoclonal antibody that targets IL-31, contributing to itch relief. The injection can be given monthly (sometimes less frequently) and the drug is associated with few side effects. Dr. Dell adds that Cytopoint can also be given to dogs that are receiving other medications for concurrent health problems.

Although atopy is manageable, most dogs need lifelong intervention, Dr. Dell says. Communicating this to pet owners and managing their expectations is a big part of a successful treatment strategy. Also, because no single drug is going to fix every allergic patient, a multifaceted approach (potentially including shampoos, ceramides, fatty acid supplements and so on) is best in most cases.

References

1. Seppänen RTK, Kaimio M, Schildt KJM, et al. Skin and ear health in a group of English bulldogs in Finland-a descriptive study with special reference to owner perceptions. Vet Dermatol 2019;30(4).

2. Dell DL, Griffin CE, Thompson LA, et al. Owner assessment of therapeutic interventions for canine atopic dermatitis: a long-term retrospective analysis. Vet Dermatol 2012;23(2):228-e47.

3. Plant JD, Neradelik MB, Polissar NL, et al. Agreement between allergen-specific IgE assays and ensuing immunotherapy recommendations from four commercial laboratories in the USA.” Vet Dermatol 2014;25(1):15-e6.