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Itchy Dogs! Atopic Dermatitis (Allergies) in Dogs, Part I

April 23, 2019

Ah, spring. Warmer weather, longer days, a vacation from snow, and… itchy dogs? It’s true, with warmer weather we commonly see a spike in seasonal allergy symptoms in dogs. So it’s a perfect time to review environmental allergies (also called atopy or atopic dermatitis) in dogs. My dog Squash has atopy, so this is a topic near and dear to my heart. This week we’ll cover what allergies are and what the common symptoms are.

Squash when his skin is quiet and comfortable.

Whether you’re a dog or a person, allergies start with a genetic predisposition to a defective barrier. Normally harmless airborne substances such as pollen, mold spores, or dust particles we call allergens are able to sneak through this barrier. The first time this happens, special cells that live in the skin collect the allergens and bring them to the immune system. Through a complex system of communication, the immune system becomes reactive to these allergens and the next time they sneak through the barrier, they are treated as invaders; among other responses, chemicals called cytokines that trigger itching and inflammation are released.

In people, this defective barrier is most commonly in the respiratory system which is why typical symptoms include runny nose, sniffling, and sneezing. In dogs, this defective barrier is most commonly in the skin and the typical symptoms are licking, scratching, rubbing, chewing, and shaking the head. (Although just to keep things interesting, people can have allergic skin disease and dogs can have allergic respiratory disease).

The most commonly affected areas of the body in dogs include the feet, ears, “armpits,” belly and inner thighs, around the eyes or mouth, and the skin around the anus. Any individual dog may have only one, a few, or multiple areas affected. Secondary yeast or bacterial infections are common due to inflammation and scratching, which allow these organisms to reach deeper than the surface of the skin.

Squash’s whole belly is red and the multiple small red spots are caused by a superficial bacterial skin infection called pyoderma, a common consequence of allergies. His belly is where he typically has symptoms, the rest of his body is usually unaffected.

We do not have a nice, neat diagnostic test for atopic dermatitis. We diagnose it based on excluding other causes of symptoms (such as fleas, mites, fungal, or hormonal diseases of the skin) and by history and clinical signs. Similar to people, there is allergy testing available, both blood and skin tests, but these are not used as diagnostic tests. Rather, they are used in animals who already have a diagnosis to guide a type of treatment called hyposensitization (“allergy shots”).

These are the typical clinical signs of atopic dermatitis in dogs:

  1. Itchy dog! This can look like scratching, licking, chewing/ nibbling/ biting at the skin, rolling or rubbing against surfaces, or head shaking if the ears are involved.
  2. Age of onset of symptoms is relatively young; 70% of dogs first show symptoms between 1 and 3 years old.
  3. Breed may increase the suspicion of atopy, as it is found more commonly in certain breeds (although any breed or mix can be affected).
  4. Symptoms improve rapidly on cortisone-type steroids.
  5. Chronic, recurrent skin and/or ear infections which may include changes to the pigment and/or thickness of the skin over time.
  6. Front feet and/or ear flap involved in symptoms even without ear infections (red, itchy ear flap).
  7. The topline and lower back are usually NOT involved; however, classically fleas will usually cause symptoms primarily on the lower back.
  8. Seasonal symptoms: There are dogs who have year round allergies (if allergens include things like dust or house molds), but many dogs in our state don’t have symptoms in the winter. An individual dog may have allergies at very specific times, or from early spring clear through the first freeze of the following fall/winter. Typically we see spikes of symptoms in early spring and late summer/early fall.
  9. A pattern of the above symptoms that cannot be correlated with a specific activity or exposure. (Sometimes contact with certain plants or other irritants such as bacteria or algae can cause symptoms similar to atopy, but can usually be correlated to things like swimming in a particular pond or playing in a particular park or field.)
The red streaks in the crease of Squash’s back leg is caused by staining of his fur from licking his itchy skin as well a previous secondary yeast infections.

Although food allergies have gotten a lot of attention in recent years, airborne environmental allergens are by far the most common cause of allergic skin disease in dogs. It is always best to rule out food allergies with what we call a feeding trial (I will cover this in detail in a separate post about food allergies), but there are a few clues: First, usually food allergies start later in life; around 5 years rather than 1-3 years. Second, food allergies have an inconsistent response to cortisone-like steroid treatment. Third, food allergies often (but not always!) have a digestive component to their symptoms (vomiting, diarrhea, constipation, gassiness, etc). Fourth, food allergies are usually year-round and environmental allergies are usually seasonal in Minnesota with a break in the winter. However, dogs with multiple allergens or with “indoor” allergens can go against this pattern.

Next time we’ll talk about management and treatment options for dogs with allergies, but feel free to call the clinic with any questions!

Karen Christopherson DVM CVA

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