Atopic dermatitis, or atopy, is a common allergic condition affecting the skin of dogs (and some cats).
Potentially anything can trigger an allergic reaction, ranging from dust mites in bedding to plant pollens in spring and food proteins in the diet.
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Atopy acts similarly to hay fever in people, except that instead of sneezing and runny eyes, symptoms in dogs include itchiness and inflamed skin. This is a complex condition, and treatment is often a matter of control rather than cure.
Following are 5 things you should know about atopic dermatitis in dogs and cats:
Atopy is itchy! Pets with atopy chew themselves, scratch constantly and rub their faces excessively.
An atopic dog will keep you up with a symphony of itching and scratching if he spends the night in your bedroom.
Typically, dogs are so itchy that they chew the skin and damage it, leading to patches of hair loss and secondary infections. Paws, legs, belly and face are usually the itchiest (pretty much everywhere except for the back).
Perhaps you have seen white dogs, such as Westies or Bichons, with brown staining on their paws; this is from excessive licking leading to saliva staining. This is a giveaway that the dog has skin irritation, most likely as a result of atopy.
Some dogs have a bizarre reaction where mainly their ears become sore and inflamed. Any dog who regularly has inflamed ears or ear infections should be assessed for atopy.
Atopic dermatitis is caused by an overactive immune system.
Dogs absorb allergens through the skin, so when an allergen comes into contact with the skin, it primes the immune system. The latter then releases antibodies to fight and control the irritant, but this releases a cascade of chemicals that result in inflammation and therefore itchiness.
When a dog encounters a particular allergen for the first time, he probably won’t react because he is not yet sensitized.
Repeat exposure, however, primes the immune system — which eventually reaches a threshold level and symptoms then occur. Many atopic dogs are younger than 3 years old when they first show signs, which frequently get worse with age.
Diagnosis can be a thorny issue and not as straightforward as you may suppose.
Skin biopsies are largely unhelpful (other than to rule out other causes of skin inflammation) because they tend to show a nonspecific inflammatory picture rather than a specific diagnosis.
Various blood tests and intradermal tests are available, and while helpful, the results can be confusing. This is because they measure the levels of antibodies to specific allergens, which do not necessarily directly correlate to the itch level (so false negatives and false positives can occur).
The distribution of the lesions (paws, legs, face and tummy) is a strong indicator of atopic dermatitis, but other conditions — such as sarcoptic and demodectic mange, ringworm, skin cancer and autoimmune disease — must be ruled out before trying atopy therapies.
In the video below, Dr. Wayne Rosenkrantz, DVM, DACVD, discusses more about atopy in dogs:
In the short term an itchy dog needs swift relief to prevent himself from damaging his skin.
Corticosteroids are a potent anti-inflammatory and highly effective at relieving itch in the short term. However, they are associated with side effects, so other long-term therapies, such as immunotherapy vaccines, or other modern drugs such as oclacitinib (Apoquel), should be considered.
Decreasing exposure to potential allergens is an important factor, and regular vacuuming to remove house dust mites and avoiding triggers, such as cut grass, are sensible measures.
Removing allergens from the coat by regular shampooing with an appropriately medicated product helps. The effect of antihistamines is disappointing in the dog and cat, but these are largely safe drugs, so there is little to be lost by trial therapy.
It is possible to develop a bespoke immunotherapy vaccine containing the allergens to which your pet reacts.
The idea is to inject small doses to desensitize the immune system and gradually build the exposure. This works really well in some pets, but unfortunately around 60 to 70% do not respond well and still need medications to settle flare-ups.
- “A prospective study on the clinical features of chronic canine atopic dermatitis and its diagnosis.” Favrot, Steffan, Seewald & Picco. Vet Dermatol, 21: 23–31.
- “Results of allergen-specific immunotherapy in 117 dogs with atopic dermatitis.” Schnabl, Bettenay, Dow & Mueller. Vet Rec, 158: 812–815.
This pet health content was written by a veterinarian.
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