Atopic Dermatitis in Cats and Dogs

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Could my dog or cat have atopic dermatitis as a cause of itching and/or recurrent infections?

Atopic dermatitis is the most common cause of itching in pets in Minnesota, if your pet is on a good flea and tick prevention.  Especially in warmer areas of the United States, or if your pet goes outdoors without a flea and tick prevention, fleas and parasites are a more common cause for itching.   A consultation with a veterinarian is warranted to rule out parasites or other skin diseases prior to making the diagnosis of atopic dermatitis. 

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Why does my pet have atopic dermatitis?

In dogs, there is strong evidence for a genetic skin barrier defect that allows allergens to penetrate the skin and trigger allergies.  Genetics are also related to the how the immune system works.  In pets predisposed to atopic dermatitis, the immune system over-reacts to allergens, which triggers inflammation of the skin and itchiness, which worsens the skin barrier, if it wasn't already defective.  A poor skin barrier, Itchiness, and inflammation predispose to recurrent infections of the skin.

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Symptoms of atopic dermatitis in dogs and cats

Dogs

Atopic dermatitis in dogs typically starts with symptoms between the ages of 1-6 years, but may start as puppies.  Symptoms can wax and wane, but in dogs, symptoms typically worsen up to the age of 6 and level off.  As dogs with atopic dermatitis get older, they tend to get more frequent infections along with itchiness.The main symptoms of atopic dermatitis in dogs are itching and recurrent infections of the skin and ears.   Dogs relieve itch by licking, chewing, scooting, rubbing, or scratching.  Dogs rarely perform these behaviors out of boredom or anxiety, although being bored or anxious makes things worse.  Infections are typically yeast and/or bacterial infections of the skin and ears.  The ears may be the only affected area in some pets.  Another area typically affected is the feet.  If you look between the toes you may notice the skin there is red or your dog chews the feet or licks the legs.  Then the armpits, abdomen, chest, under the neck, and anal area are often affected- the skin may be red, greasy, smelly or itchy.  With long term issues, the skin becomes darker and become thicker.  The hair may be missing or shorter due to infections and chewing.  Some terriers have their worst symptoms down their backs.  Some dogs lick huge sores on their lower legs.  Some dogs have red, runny eyes and may sneeze due to allergies.

Cats

Cats are usually over 1 year of age when symptoms start.  The main symptom of atopic dermatitis in cats is itching.  Cats will scratch, bite their skin, pull out hair, and overgroom to help relieve itch. Cats rarely perform these behaviors out of boredom or anxiety, although being bored or anxious makes things worse.  Cats with atopic dermatitis get skin and ear infections much less often than dogs do, but they certainly occur.  Cats most often make bald patches on themselves, usually the lower abdomen is the worst area, and with progression, raw areas are created with the cat’s raspy tongue.  Cats often will scratch at the head with the hind leg and create scabs around the eyes and ears.  Cats can manifest allergies with asthma too, but it is not common to have asthma and skin symptoms at the same time.  Asthma causes coughing, and some people mistake this for "coughing up a hairball" but cats do not cough up hairballs, they vomit hairballs.

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Could my dog or cat have allergies?

Because there are immune system defects and skin barrier defects with atopic dermatitis, many pets with atopic dermatitis have allergies to things they are exposed to.  Allergies cause a flare of symptoms.  There are two basic types of allergies once fleas are ruled out- food allergy and environmental allergy.  Pets can have both of these allergy types at the same time.  

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Food allergies

If your pet had allergy symptoms start at younger than 1 year of age, the symptoms are year round, or there are any gastrointestinal signs like vomiting, loose stools, or having more than 2 bowel movements per day, food allergies are more likely.  Most pets with allergies don’t have food allergies, only about 5-10% of dogs and perhaps 30% of cats do.  There is no diagnostic test for a food allergy other than an elimination diet trial.  If a pet responds to a food trial, then we can go about the tedious task of determining exactly what they are allergic to, or we can simply find a diet they do well on and stick with it.

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Environmental allergies

Environmental allergies are reactions to allergens like pollens, dusts, and molds.  Environmental allergies may be seasonal with outdoor allergens, or year round with indoor allergens.  Most pets have a combination of indoor and outdoor allergies.  To determine what allergens in the environment are causing your pet to have symptoms, we can perform allergy testing.  There is no test for food allergens other than a dietary trial.

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Treatments for atopic dermatitis and allergies in dogs and cats

If there is a food allergy, the offending foods must be avoided.  To control environmental allergies, sometimes short courses of medications are needed.  If allergic symptoms recur quickly when treatments are stopped, long term treatments are needed.  Some pets need antibiotics and anti-yeast medications in addition to medications that control the inflammation in the skin.  When the inflammation of the skin is controlled, the itch resolves.  

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Unfortunately, there is still no cure for atopic dermatitis and allergies.  The closest treatment we have to cure allergy flares is to do allergy testing and allergy shots. Allergy shots do not cause immunosuppression, unlike some other treatments for allergies.  Allergy shots may take a while to work and so other medications like Apoquel, Cytopoint, or Atopica are needed while waiting for the allergy shots to have maximal effect.  Of course, there are adjunctive treatments for allergies, like shampoos, topical steroids or moisturizers, antihistamines, and omega-3 fatty acids. If a pet has very mild allergies, these other treatments may be sufficient.

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What combination of therapies is best for your pet depends on your individual pet, their personality, type and locations of infections, seasonality, skin and hair type, and of course what they respond best to.  It often takes several visits with a dermatologist to find the perfect combination of treatments, especially with severe cases, but our goal is that your pet ultimately has less flare ups, infections, and vet visits.  Our whole team is here to help you and your pet, to make sure your pet gets relief and you have peace of mind.

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What else could be causing my pet’s itching and infections?

There are many other causes of itching, including parasites.  For example, if ear margins are affected, and the pet is minimally or not responding to glucocorticoid (steroid) and antibiotic treatments, then your pet has a much higher likelihood of having sarcoptic mites.  If the area of the back over your pet’s back legs to the tail is affected, then your pet has a higher chance of having fleas or a mite called Cheyletiella.  Skin infections with yeast and/or bacteria can be very itchy.  The underlying reason why your pet got an infection in the first place should be investigated- if your pet is young and has recurrent infections, the most likely cause is atopic dermatitis.  There are other diseases we would need to rule out if an older dog or cat suddenly develops itching or infections.  Sometimes dogs and cats focus on a particular area due to pain- like licking an arthritic paw, or licking the lower abdomen with bladder stones.  A thorough history, physical exam, diagnostics, and response to treatment help to confirm a diagnosis.

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