Visiting Veterinarian

Visiting Veterinarian

Scratching the itch

By Michele Gerhard Jasny V.M.D. - January 5, 2006

It happens at least once a week. An owner brings her dog, Itchy, in to see me because he's scratching. I run a flea comb over him. If I'm lucky, I find fleas...or at least flea dirt. (That's the polite term for flea excrement, which looks like specks of black sand.) Fleas are easy. His owner has no trouble grasping the idea that those hopping biting insects make Itchy scratch. She is delighted with my easy solution. I hand her a pack of Advantage or Frontline. "Apply this once a month. You're done." But since the advent of those wonderful flea control products, I am rarely blessed with such a simple and succinct diagnosis and treatment. Nope, Itchy is flea-free and itchy all over. I may do a skin scraping to rule out other parasites, like sarcoptic mange mites, but once we rule out these pesky bugs, I hit the mental "Play" button in my brain that starts my Atopic Dermatitis Rap.

Atopy is a common skin condition in dogs caused by an allergic reaction to environmental substances such as pollens, dust mites, and molds. As many as 10 to15 percent of dogs are affected. Exposure occurs via inhalation or direct absorption through the skin. A genetic component is suspected, and certain breeds are predisposed to atopy, but I think I've seen it in just about every kind of dog. Signs usually develop between the ages of one and three years but have been reported in dogs as young as three months or as old as seven years. The main sign is scratching...and chewing, licking, biting, and rubbing ...and did I say scratching? Itchy may scratch at his face, legs, ears, belly, and feet. Hair loss and secondary skin and ear infections are common. Some dogs develop conjunctivitis, runny eyes, and sneezing.

"What do you think he's allergic to, Doc?" his mom always asks. "I dunno," I say. "Let's sit around and guess for an hour. I don't have anything better to do." No, I don't actually say that. What I do say is "Without allergy testing, I can't tell for sure." Nobody wants to hear this. Everyone wants to blame the new carpet, the poison ivy, the cats. Not likely. The common canine allergies are things that are harder to eliminate. Canine atopy is generally seasonal, at least in the beginning. Itchy scratches in the spring and fall? Sounds like pollen allergies. Wintertime itchiness? House dust mites and molds. Many dogs have multiple allergies. Did I mention that if you want to know for sure, you need to do the tests?

Trial and error

At this point most owners ask if changing foods would help. Well, sure, if Itchy has a food allergy. We can test for a food allergy, which tends to cause year-round symptoms. We can try a hypoallergenic food trial for six to eight weeks. But randomly changing brands isn't useful. The question is usually prompted by a desire for a quick "cure." Sorry. Allergies don't go away. In fact, they usually get worse year by year. The good news is that even if we never pin down the specific offenders, we can treat symptomatically with antihistamines, essential fatty acids, cortisone, and topical therapy like shampoos, sprays, and rinses.

Antihistamines have few side effects, are very safe, and many can be purchased over-the-counter. The trouble is that no single antihistamine has proven to be consistently effective. Different antihistamines work for different dogs, and in many cases, no antihistamine provides adequate relief. Most need to be given two to three times daily and you need to give each drug a solid two week trial period before deciding if it is useful. Essential fatty acids, specifically omega-3s that contain eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are thought to be beneficial, directly reducing itchiness and increasing the effect of antihistamines. Topical treatments can be effective but are labor-intensive and not very long-lasting. Baths help remove allergens from the coat and shampoos deliver soothing medications such as oatmeal or aloe vera directly to irritated skin. Shampoos, leave-on rinses, and sprays are available containing antihistamines, antibacterials, anti-itch chemicals, even corticosteroids. I have mixed feelings about all these. Asking an owner to wrestle an 80-pound shaggy dog into the tub on Monday, only to have him scratching madly again by Thursday, may not put me in her good graces. On the other hand, some owners happily pop their pups in the bath on a regular basis with minimal hassle and good results. Too much bathing, however, may dry the skin and exacerbate the problem.

The cortisone dilemma

Which brings us to cortisone, properly called corticosteroids. The most commonly used are prednisone or prednisolone. If used correctly, they can provide simple, effective, inexpensive symptomatic control for many dogs. The problem is that corticosteroids can have serious side effects, both short and long-term, especially if not used with discretion. Some owners are irrationally afraid of cortisone. Others do not take the warnings seriously enough. Honestly, I love prednisone. It's cheap. It's easy to give. It works. For seasonal atopy, I'm all for low-dose oral prednisone, starting with a loading dose and gradually decreasing to an alternate-day basis for short-term maintenance. But if Itchy starts needing more and more prednisone, for longer and longer periods, it's time to look into other options.

There are two ways to allergy test: intradermal testing (IDT) and serum allergy testing (SAT). IDT testing involves injecting tiny bits of various allergens under the skin and looking for reactions. You should go to a veterinary dermatologist for this. SAT testing, on the other hand, can be done easily by your regular veterinarian. We just draw blood and send it to a laboratory. SAT is a little less accurate than IDT but usually adequate if a reliable laboratory is used. Once we identify Itchy's specific allergies, we can address them in two ways: avoidance and immunotherapy, also called hyposensitization.

Avoidance is ...avoidance. There are numerous steps you can take in your house to reduce mold including dehumidifiers, replacing carpets with hardwood or linoleum, frequent changes of heating and AC filters, professional furniture cleaning, and getting Itchy outside as much as possible. House dust mites can be lessened by frequent vacuuming, using hepa filters, mopping, and minimizing carpets, drapes, and dust-collecting knickknacks in the environment. Pollen avoidance is tougher, unless you're ready to relocate to, say, the desert.

Hyposensitization means giving Itchy injections of serum. Over three to six months, he is injected with gradually increasing amounts of an allergen solution. Your vet can teach you how to give the shots. Hyposensitization reduces itching in 65-70% of patients. Injections usually begin twice weekly and eventually can be reduced to every two to three weeks. Itchy may still need other medication periodically to control his symptoms, but hyposensitization will usually reduce the need.

Finally, if none of this work to stop Itchy's itching, there is a new medication called Atopica that can be used. A potent (and pricey) immunosuppressant, this drug should be reserved for cases that don't respond to conventional treatment.