The nuts and bolts of canine atopic dermatitis

Mitchy / stock.adobe.com

Canine atopic dermatitis is the second most common allergic skin disease in dogs after flea allergy dermatitis.¹ In an interview with dvm360®, Julia E. Miller, DVM, DACVD, described this condition, also referred to as atopy or environmental allergens, as a genetic predisposition to be hypersensitive to normally innocuous substances in the environment.

“This is something that when you’re in general practice, you see it every single day. When you’re a dermatologist, we certainly see it every day—it is exceedingly common,” Miller said.

Breeds predisposed and age of onset

Miller explained that because atopic dermatitis is a genetic predisposition, it’s simply a matter of time before the clinical signs appear. “Essentially, these animals are born with this predisposition to being overly sensitive to things in their environment. And it’s just kind of a ticking time bomb waiting for it to show up,” she said.

The typical age of onset for atopic dermatitis is between 6 months and 3 years, and specific breeds—golden and Labrador retrievers, pit bull terriers, pugs, boxers, and German shepherds—have an increased risk of developing it.² However, Miller said, atopy can be present in any breed, including mixed breeds.

Primary and secondary clinical signs

Andrew Rosenberg, DVM, DACVD, shared his knowledge on this prevalent chronic condition in dogs during a presentation at the 2021 New York Vet Show in New York, New York. Rosenberg explained that the most common skin areas affected by atopy are the pinna, axilla, front paws, hind paws, lips, and paranal. In contrast, Miller said, “With most of our environmentally allergic dogs, the area on the body that gets spared, the area they don’t itch at or don’t target, is usually along the dorsum.”

The primary clinical signs of atopic dermatitis include erythema and pruritus, and the secondary signs include excoriations and infections, Rosenberg said. In addition, common infections caused by this disease are staphylococcus infections and Malassezia dermatitis, Miller said.

Rosenberg said it’s equally important to note that there are no pathognomonic signs and that other skin diseases must be ruled out before making the diagnosis. Miller said the main condition atopy mimics is ectoparasites. “When I have a dog come in that is itchy…my No. 1 rule out is always fleas. And sure, it could be environmentally allergic. That’s possible. But I better rule out ectoparasites every time,” she said.

She added that atopic dermatitis can also look like scabies or a food allergy, which present in an almost identical manner. She advises veterinarians to rely heavily on history taking and diet trials.

How to diagnose a potentially atopic condition

Perform a cytology or culture test

Both Rosenberg and Miller emphasized starting an examination for a potentially atopic patient with a cytology or culture test. This allows veterinarians to treat any secondary infections, whether they be yeast or bacterial.

“I really can’t stress enough to do your cytologies. That should be the first thing you are doing when you’re presented with an atopic dog,” Rosenberg said. “Don’t be afraid to culture [a] skin infection; it’s never wrong to do so. If you see raw bacteria, you should be culturing, and if there’s a bacterial infection that’s not resolving with antimicrobial therapies, you should be culturing.”

Miller added that if veterinarians simply focus on the allergies and not the secondary problems, it can cause them to be less successful in their treatment.

“I always recommend that you do cytology on every dog because you have to treat those secondary problems and treat them aggressively. Otherwise, you’re never going to get control of the itch. And then you’re never going to get control of the environmental allergies,” she said.

Identify the underlying allergy

It is also key to determine which environmental allergy is affecting the patient so treatment methods can be incorporated for this as well. “It would be great if we could get to the root cause of what the dog is allergic to and manage that,” Rosenberg said. Among the common allergens that cause a dog to develop atopy are pollens, mold spores, dust mites, shed skin cells, and insect proteins.³

Miller said there are 2 ways to allergy test animals: through a blood (serum) test—where you draw blood and submit it to a laboratory to have immunoglobulin E levels examined—or an intradermal allergen (skin) test—where you sedate the patient and inject the allergen directly under their skin to see if hives form. Miller said dermatologists don’t recommend saliva or hair tests because they are not always accurate.

“The gold standard for what most people consider the best choice for allergy testing is the intradermal skin test,” Miller added. “But dermatologists out there certainly use both intradermal and serum allergy testing. I always recommend, wherever you practice, [that you] talk to the dermatologist in your area, find out what they’re doing and what they recommend.”

Treat the secondary infection and allergen

Secondary infection

Once the pet is diagnosed and it is determined that there is a yeast or bacterial infection, treating the secondary infection is vital to significantly reduce pruritus, Rosenberg said. “My principles for treating secondary infections…we’re getting away as much as we can from systemic antibiotics with all the resistance…so if there’s [a] focal infection, I encourage you to use more topical therapies. For widespread infection, we still use antibiotics,” Rosenberg said.

“I always recommend [prescribing an antibiotic for] at least 3 weeks, many times 4 weeks, and the general rule is to treat with an antibiotic for 1 week beyond a clinical cure so you treat until everything looks normal and then add on a week,” he said. “I always recommend rechecking these patients before stopping [the] antibiotic.”

Environmental allergens

Steroids

One method for treating dogs with environmental allergens is to use oral steroids, which Miller referred to as “tried-and-true oldies but goodies.” They calm the immune system, are effective for most animals, and have few adverse effects.

“[With steroids] we stop the inflammation in the skin, because that’s going to stop the itch and then they don’t get their secondary infections,” Miller explained. However, steroids are not a good long-term protocol for dogs, and atopy is a lifelong disease.

Immunotherapy

For a more long-term approach to managing atopic dermatitis, you can incorporate immunotherapy. With this holistic method, allergy shots are created based on a pet’s specific allergies and then injected into the skin to address the root of the problem.

For example, Miller said, “Say [the dog] is allergic to ragweed, it’s allergic to [some] kind of grass, and it’s allergic to [dander from] humans. We put those 3 things in a vial and then we can either inject that into the skin or we can do it under the tongue, so we can do injectable immunotherapy or sublingual immunotherapy….It’s just like what they do in humans. We’re trying to kind of rewire the immune system of that animal by exposing them to that allergen all the time, with the hope that then they won’t be quite so sensitive.”

The downside to immunotherapy is that it takes a long time to reregulate the immune system, approximately a year, according to Miller. Therefore, the clients must be willing to put in the effort and have the patience to pursue this treatment for their pet.

References

1. Elfenbein H. Atopic dermatitis in dogs: causes, symptoms, and treatment. PetMD. February 13, 2020. Accessed November 8, 2021. https://www.petmd.com/dog/conditions/skin/c_dg_atopic_dermatitis
2. Miller WH, Griffin CE, Campbell KL, eds. Hypersensitivity Disorders. In: Muller and Kirk’s Small Animal Dermatology 7th ed. Elsevier; 2013:372.
3. Barnette C, Ward E. Allergies in dogs. VCA Animal Hospitals. Accessed June 29, 2022. https://vcahospitals.com/know-your-pet/allergy-general-in-dogs