A dog that licks or chews on its feet, rubs its face as if itchy, scratches under its front legs and in the groin area, and licks its anal area excessively may be telling you that it has atopic dermatitis. It starts with a little inflammation, then generalized itching, called “pruritis,” leading to scratching. Next comes hair loss, often followed by a skin infection with bumps.
“The immune system is overreacting to something,” says Patrick Hensel, Dr.med.vet., a diplomate of the American College of Veterinary Dermatologists and associate professor of dermatology at the University of Georgia College of Veterinary Medicine in Athens.
Chronic atopic dermatitis is almost always due to an allergy of some kind, and typically begins between 6 months of age and 3 years.
“Every dog [who has it] is allergic to something,” says Hensel, who received his veterinary degree in Germany. “The problem is to figure it out. It can be tricky.” For most dogs, a source of the allergy such as a food ingredient or something in the environment can be identified. Sometimes it starts with the bite of an insect, such as a mosquito or even a fly.
If your dog has clinical signs of atopic dermatitis, the particular cause will be dependent on where you live. “Here in the Southeast, we have a totally different set of allergens than in the West,” Hensel says. To complicate matters further, a combination of things can cause the allergic reaction and genetics also play a role, he adds.
Chinese Shar-Pei, Wire Fox Terriers, Golden Retrievers, Dalmatians, Boxers, Boston Terriers, Labrador Retrievers, Lhasa Apsos, Scottish Terriers, Shih Tzu and West Highland White Terriers can be predisposed to atopic dermatitis, but Hensel says there is no official recommendation regarding the breeding of dogs with allergies. A lot depends on when a particular dog is exposed to a specific allergen, he says. The Merck Veterinary Manual notes that “prevalence within a breed is largely dependent on the genetic pool and region.”
Although neither the American Veterinary Medical Association nor the American College of Veterinary Dermatologists currently has an official recommendation, Hensel says that a breeder with a severely allergic dog should consider not breeding it.
In the Southeast where Hensel teaches and practices, at least 90 percent of his dermatitis patients have one or more allergies. Part of that high number, however, is because of the humidity and heat in that part of the country. “We are a high-allergy region in general,” he says.
When a dog shows up at his veterinary college clinic with signs of atopic dermatitis, “The first thing we do is rule out other diseases, parasitic diseases” or any skin infections. “If we rule that out, and these animals are still pruritic, then the next step is to rule out a food allergy.” Food and environmental allergies “look very, very similar,” he says.
While research says that about 10 percent of dogs with atopic dermatitis have food allergies, “I personally believe it’s much higher,” he says. More than that percentage of the dogs seen at the university clinic have food allergies. Hensel thinks that’s because of the protocol the dermatology team follows. “You get a higher response when you follow it strictly.”
First the dog is fed something it has never eaten before, such as rabbit or kangaroo, called a “novel protein.” A hydrolyzed diet, one in which protein such as soy or chicken are pre-processed, can also be used. However, Hensel says it’s important to use a veterinary prescription diet, rather than an over-the-counter one, because ingredient control is more stringent. The dog must eat this restricted diet for a minimum of eight weeks, he says. During this time, it can have no table scraps and no dog treats of any kind. Even medication in a capsule – if the capsule is made of gelatin – can alter the test results. “Then we can start introducing ingredients,” Hensel says, with the team “challenging” the dog with its previous diet to see if clinical signs of the dermatitis re-emerge.
Chicken, beef and dairy products are the most common food allergens, he says, with a dog “occasionally” reacting to corn or soy.
If the dog ultimately reacts to an ingredient added back to the diet, it will “dramatically help” if it doesn’t eat that ingredient in the future. The dermatitis may be controlled simply by never allowing the dog to eat that item again. However, “Even though we say it’s controlled, it doesn’t mean they’ll always be normal,” Hensel says. For example, the dog may go along fine for months or longer, then get bitten by a flea, and again, the dermatitis will flare up.
When that happens, an antihistamine, such as Benadryl, may be enough to get the inflammation under control and stop the reaction from growing. Or it may not, but a few days of prednisone tablets should clear it up, Hensel says.
Then the dog will be fine again, until there’s some other assault on its immune system.
If the food allergy test reveals no allergy, the next step is to test for environmental allergens.
House and Yard
Pollen, grasses, trees, dust mites, danders and all kinds of things can cause an allergic reaction, resulting in atopic dermatitis.
Tests to identify which one is affecting an individual dog come in two forms, Hensel says. The preferred is a skin test. Simply put: “You inject a small amount of allergen into the skin, then see if there’s a reaction,” he says. However, most non-specialized veterinary practices use allergy tests performed on the dog’s blood to look for allergen-specific antibodies. “Neither test is perfect,” he says, “but we believe so far that skin tests are more reliable than blood tests.”
Once the dermatologist knows what they are, desensitization, referred to as “allergy shots” begins.
Such skin tests often determine that a dog has a combination of allergies. Photo courtesy of Patrick Hensel, Dr.med.vet.
Although it can vary depending on the patient, Hensel says, most dogs receive injections with increasing amounts of the allergen every other day for 25 days, then once a week. “There’s a 70 to 80 percent success rate” with this method, leading to at least a 50 percent improvement in clinical signs. “Again, it’s not perfect,” Hensel says. It may take six to nine months for that improvement to take place. Once it does, the dog is rechecked every three months for a year. “We then decide whether we want to continue or stop it. If there is complete control, we reduce injections to every other week. The question is can we take them off the vaccine at some point? Many clients don’t want to go off after the animal is under control.”
If the decision is made to discontinue the allergy shots, occasional flare-ups can be expected. The goals then are “to keep the animal comfortable, reduce their itch and inflammation,” Hensel says. Again Benadryl can defuse the flare-up, but if not, prednisone usually does the job.
For dog owners who don’t want to go through the intense process of desensitization, the cyclosporine “can be effective for long-term control,” Hensel says.
When Nothing Works
Unfortunately, approximately 10 to 20 percent of dogs’ dermatitis has no identifiable cause. In those cases, it’s a matter of keeping the inflammation down as much as possible and trying to keep the dog as comfortable as is realistic.
Fortunately, atopic dermatitis is a “hot potato” in veterinary dermatology, Hensel says, so there’s a lot of research going on at lots of veterinary schools all across the country and internationally. That research is looking at the condition on all fronts from how to better diagnose allergies to topical drugs that might help dogs whose allergies can’t be identified to a “big push,” Hensel says, to create a skin barrier to prevent allergens from invading through the skin.
Right now, “there are products to basically restore the skin barrier,” he says. Some you apply with an applicator; another is a spot-on that you apply weekly after a bath. “As an adjunct treatment, they are often beneficial,” he says. “Clients say the skin is less dry, and the coat is shinier.”
Despite prevalence of atopic dermatitis and all of the interest in it within the veterinary research community, “We still don’t know a lot,” he says. “We know the basics, but it’s a much more complex thing than we believed it was.”
Dogs that have been diagnosed also benefit from eating a high-end diet with a high fatty-acid content, he says. And it’s important that they remain on a diet that works for them, without the addition of treats or table food that aren’t hypoallergenic for the particular dog. While there is some suggestion that probiotics can be helpful, he, personally, hasn’t had any experience with them. Depending on where the dog lives, it may need year-round flea preventives. A house with fewer rugs, draperies and carpeting can help, as they can trap allergens, creating more exposure.
“Every patient is different,” Hensel says, so finding what works and sticking to it are the keys to control.