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Veterinary Forum May 2008 (Vol 25, No 5)

Clinical Report: Atopic dermatitis—every little bit adds up

by Sophia Yin, DVM, MS (Animal Science)

    A common misstep generalists make when diagnosing atopic dermatitis is to rely on an intradermal skin or serum test to make the diagnosis, according to dermatologists. The experts say they understand that the serum test is quick and easy when the waiting room is full, but atopic dermatitis should be diagnosed by considering the clinical signs and history of the animal.

    "The only reason for doing an allergy test is if you are going to put the animal on immunotherapy," explains Lowell Ackerman, DVM, DACVD, MBA, MPA, clinical professor of dermatology and allergy at Tufts University Cummings School of Veterinary Medicine in North Grafton, Mass. "There is no diagnostic test for atopic dermatitis. It's a judgment call that is made in the exam room based on age, breed and clinical presentation."

    One strategy, he adds, is allergen avoidance, which can be done more easily with indoor allergens because it is near impossible to avoid pollen.

    Rosanna Marsella, DVM, DACVD, associate professor of veterinary dermatology at the University of Florida College of Veterinary Medicine in Gainesville, agrees. The test, she says, is to determine which allergens to include in the vaccine.

    Ackerman says that both serum and skin testing have their place in determining the immunotherapy mix, but there is variability among laboratories that interpret the serum test and make the vaccine.

    "When each lab is deciding what they are going to use as their test substance, there is variability, as each lab uses different allergens and, in some cases, different techniques," he explains.

    "There is nothing wrong with that. I use the blood test. It is simple to do, but it takes more work to interpret the results — blood tests tend to yield more false-positive results than intradermal skin testing does, so you need to be careful in correlating the results with the clinical history of your patient. Just remember, we are treating animals, not lab results."

    Ackerman adds that veterinarians should spend time deciding what goes into the immunotherapy serum. "The only allergens that should go into the immunotherapy mix are the ones that agree with the animal's clinical history. The biggest mistake that most veterinarians make is when they tell the lab, 'Put whatever is positive into the treatment mix.' You dilute the important allergens when you do that."

    Treatment

    Corticosteroids still have their place in atopic disease management, the experts say. The drugs work well, temper the flare-up and provide immediate relief, but try to use the lowest dose possible to avoid adverse effects. Ackerman says he likes Temaril-P (trimeprazine"prednisolone, Pfizer Animal Health) because it allows lower dosing.

    Marsella adds that immune modulators, such as cyclosporine (Atopica, Novartis Animal Health), signal a new approach for atopic disease — to modulate the inflammatory factors rather than just control or suppress inflammation.

    "Although we have this effective drug available, it is not a substitution for a workup," warns Marsella, who is a member of the Veterinary Forum Editorial Board.

    Researchers hope to eventually develop treatments that modulate the barrier function of the skin, but for now a multimodal approach is best. There are many options, including immunotherapy, corticosteroids, cyclosporine, antihistamines, fatty acids, shampoos, lotions and creams, etc. "Soothing products that we have been using contain phytosphingosine, one of the key elements of lipid composition," Marsella says, adding that these products can improve the lipid composition of the skin.

    However, the mechanism of action remains under investigation. One clinical trial showed the antipruritic effects of this therapy, Marsella adds, "but we need to figure out how this works. At this point, modulation of the barrier function is only a hypothesis."

    "We mix and match any and all of these to get the best effect with the least amount of drugs," explains Ackerman, who also is a member of the Forum board.

    Any approach needs constant monitoring and adjustment, he says. "What I tell veterinarians about this disease is that it is no different from managing a diabetic dog or a dog with chronic arthritis. You would not take a diabetic dog, send it home with insulin and say, 'I'll see you in a year.' Even with well-controlled dogs — I see them four times a year," Ackerman says.

    Owner has to be part of management team

    Owner education is important, Ackerman adds. Veterinarians must make sure that owners realize two things: atopic disease takes time to sort out, and dogs do not outgrow it. "They need to be managed forever," he warns.

    Ackerman says that building up a tolerance, when using immunotherapy, can take a long time — sometimes up to 8 months — and that's only if it works. "The success rate is 65% to 75%, and it probably takes a year to get there," he explains. "When the animal is thumping, the answer is not 'Let's start immunotherapy.'

    "The first thing you have to do is get the animal comfortable," he says. "You don't have the luxury of waiting for immunotherapy to work. You have to manage them medically."

    Marsella adds that atopic disease should be thought of as multifactorial. "Most of the atopic dogs also have food allergy , and they often have secondary infections. Every little thing is additive, so the best thing that clinicians can do is treat all the factors."

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