Vol 8 No 4

Fall 2006

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2006 Reunion

Itchy Dogs & Allergies


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Allergies and Itchy Dogs

We’ve all seen the look of intense pleasure on our dog’s face when it itches in just the right place, and our own casual scratching of a chin or an ear can elicit a grateful lick or nudge. But sometimes itching becomes more relentless in our canine friends who are susceptible to allergies, creating considerable discomfort.

GRRI recently spoke with Dr. Karen Helton-Rhodes, who specializes in canine dermatological disorders, to find out more about allergies and how we can help provide relief.

GRRI:  Thanks, Dr. Rhodes, for agreeing to spend some time with us. All dogs itch from time to time; what kinds of symptoms should begin to suggest that there might be a problem with allergies?

Dr. Rhodes: Well, although allergies are pretty common, we might see some symptoms that would suggest allergies as one potential problem among a group of conditions that provoke similar reactions in dogs. In general we’re looking for things like intense itching, especially around the feet, face, and axillary (the “armpits”) regions of the dog’s body. The ears tend be involved as well, with otitis externa commonly presenting. If the problem is chronic, we might see thickening and changing pigmentation in the skin.

GRRI: But you’re suggesting that these symptoms don’t automatically mean that allergic reactions are involved?

Dr. Rhodes: No, not necessarily. Dogs often have other  problems, which may be secondary to  symptoms of allergic dermatitis, or may in fact be the primary problem. For example, we see cases of  malassezia in itchy dogs, which is an overgrowth of yeast. The yeast are effective opportunists that take advantage of the allergic dog’s condition; for example, dogs suffering from allergies will often produce a lot of ear wax which is a good microenvironment for yeast and bacterial overgrowth.  Other problems that you might see include staph bacterial infection of the skin and hair follicles (pyoderma), which would also create itching along with some rash, pimples, or hot spots.  Conditions like a scabies infestation (caused by a burrowing mite) or a fungal disease like ringworm would also cause a lot of itching and discomfort.

GRRI:  So how do you figure out what the real problem is?

Dr. Rhodes: Sometimes it isn’t so easy! There is some testing that we can consider, but before we discuss that maybe it would be good to think about the physiological responses a dog has to the presence of an allergen. Basically any dog, allergic or not, will produce antibodies in response to the presence of what the body will consider to be “foreign” proteins. So, whether it is pollen or mites or a kind of food or mold or whatever, the dog’s immune system begins to produce antibodies to the “invader”. We categorize the antibodies as IgE, IgG, or IgM, and what we think is going on is that allergic dogs produce significantly higher levels of the IgE category of antibodies. Some dogs tolerate higher levels of IgE antibodies better than others.

GRRI: So these IgE antibodies cause more sensitive dogs to itch?

Dr. Rhodes: Indirectly, yes. The IgE antibody will bind to mast cells in the skin. When the dog is exposed to the allergen again, the allergen will bind to the IgE antibody attached to the mast cells. This binding of the allergen will cause the mast cell to rupture, releasing chemicals (histamines, leukotrienes, prostaglandins, etc) that cause the skin to itch.

We can try to look for the specific kinds of IgE antibodies produced for each allergen in the dog’s blood; this is often referred to as in vitro testing, or serum or plasma testing. There are two general techniques for serum testing, one using a radioactive tag (“RAST”) to identify the appropriate antibody, and another using an enzyme (“ELISA”) tag . Serum testing is fairly easy and not that expensive, but I don’t usually recommend it because it suffers from poor reproducibility in tests and is susceptible to too many false positives; that is, the test indicates an allergy to a substance that doesn’t in fact provoke the problematic response. I certainly wouldn’t use a serum test for a suspected food allergy; a trial elimination diet is the only way to find the offending food.

GRRI:  So you’d feed the dog only a simple diet of what you know wouldn’t cause the allergic reaction, and gradually add things until you saw the allergic response?

Dr. Rhodes: Exactly.

GRRI:  How could you tell at the onset of the itching if it was caused by a food allergy or allergy to something else?

Dr. Rhodes: You really can’t; I told you this wasn’t easy! We used to think that food allergy symptoms were focused more on the head and ears, but over the years we’ve come to observe that this isn’t necessarily true. If the dog had gastrointestinal symptoms along with the other symptoms of allergies, we might think about food allergies first. What’s happening in those cases is that mast cells bound to allergens passing through the gut are rupturing, releasing the same irritating chemicals that promote itching in the skin.

Our usual approach is to try to look for the secondary problems like yeast or bacteria and treat them, and also rule out things like mites or fungal infections. If the symptoms didn’t change with the season, we’d start a food trial to try to identify the allergen. Seasonal symptoms might point us more towards an allergy resulting from inhalation or contact with something.

GRRI: What about skin tests?

Dr. Rhodes: Intradermal skin testing is considered the “gold standard” of allergy testing. We can inject between 50 and 80 allergens into the skin, and then measure the response of the skin to identify problems with specific allergens. One possible disadvantage to intradermal testing is that there needs to be between 2-8 weeks of abstinence from use of a variety of drugs that may interfere with the dog’s immune response. So, if a dog were being treated with these kinds of drugs for some condition, they would need to stop using the drugs for some time, which isn’t always feasible.  For an itchy dog, it is tough to pull them off the drugs that are making them comfortable; the good news is that one effective therapy for itching (cyclosporine) does not need to be terminated before a skin test.

GRRI: Can we take a shortcut here? Are Golden Retrievers particularly susceptible to specific types of allergens?

Dr. Rhodes: We don’t see any evidence of that. We do think there is genetic predisposition to allergic dermatitis in Goldens, but it isn’t specific to a particular allergen. That said, I’d note that house dust and dust mites are very common offending allergens.

GRRI: Most of us are so happy just to get rid of the clumps of dog hair floating around our houses that we don’t always get to dusting. If it is inevitable that a dog will come into contact with an allergen like dust, how can we treat the problem?

Dr. Rhodes:  We have a couple of options. Hyposensitization is a way of trying to induce immunological tolerance by injecting small doses of the allergen over an extended period of time. It is similar to the thinking behind vaccination. Most dogs tolerate the injections very well, and people get used to administering the injections pretty quickly. It isn’t a cure, but hyposensitization is a very reasonable way of managing the problem over the longer term.  The disadvantage here is that it may take many months before you begin to see relief, as the sensitization process is a pretty slow one.

We also have a variety of drugs that may relieve symptoms. Antihistamines seem to be effective in about 50% of allergic dogs; the challenge is to find the right drug for each particular dog. Typically we have our clients begin trials of over-the-counter antihistamines, with the idea being to observe the dog’s reaction for a week or two before deciding on its effectiveness. If over-the-counter drugs aren’t useful, we can move on to some prescription antihistamines. If those aren’t helpful, we’ve had a lot of success with a drug used in human organ transplants to help reduce organ rejection; cyclosporine works well and doesn’t have some of the negative side effects of corticosteroids, but unfortunately it is quite expensive.

GRRI:  What about nutritional support?

Dr. Rhodes: Well, the data is a little soft, but there is at least some evidence that essential fatty acid supplementation may be helpful in about 25% of the cases. The EFA’s act as an anti-inflammatory, and since there isn’t any harm in supplementing a dog’s diet with them other than the expense, I’d certainly try it.

GRRI:  How about the sprays or creams we see for itching?

Dr. Rhodes: We will often suggest use of a spray that has a very low dose of triamcinalone, which provides temporary relief of severe itching. Many of our patients are on a regular shampoo regimen as well, which is especially effective at addressing some of the coincident problems like yeast or bacterial infections that we talked about earlier. It really is amazing what a difference something as simple as a Selsen Blue shampoo two or three times a week can make in those cases.

GRRI:  It sounds as if we have at least a couple of good options to relieve the discomfort that allergies can cause. Dr. Rhodes, thanks so much for speaking with us.

Dr. Karen Helton-Rhodes has practiced as a board-certified veterinary dermatologist in the tri-state area since 1982. As head of the department of dermatology at the Animal Medical Center in New York for 12 years, she actively participated in the training of the interns and residents. Dr. Helton-Rhodes also held the position of Assistant Clinical Professor of Dermatology at New York University Hospital from 1985 until 1997. This position facilitated communication and research opportunities in the area of comparative dermatology. She received the Merit Award from VMA of NYC in 1991, Clendenin J. Ryan teaching award in 1992 and was honored by being listed as one of the “Best Veterinarians in New York” by New York Magazine in 2002. In 1994 she joined a specialty group in New Jersey, Animal Emergency and Referral Associates. As the practice grew, Dr. Helton-Rhodes developed an affiliate practice, Veterinary Referral Centre, located in Little Falls, New Jersey as the primary location of her referral practice (1-888-722-7200).

Dr. Helton-Rhodes has lectured extensively on the topic of veterinary dermatology, allergy, immunology and dermatopathology. She is the author of numerous textbook chapters, medical journals articles, and has authored a veterinary textbook entitled "The 5-Minute Veterinary Consult: Clinical Companion in Small Animal Dermatology."