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Dear Dr. Walt: It never fails - this time of the year my yellow lab's favourite pasttime is scratching. This inevitably leads to sores and something that the veterinarian calls a 'hot spot' - a nasty open, oozing sore that my dog simply won't leave alone. My vet always talks about allergies and suggests testing to confirm; however, I'm skeptical. What are your thoughts?

From rashes to bumps, redness to 'hot spots', and itching to chewing, the theme of your e-mail has been repeated numerous times in my in-box as of late. While there are a host of different causes of skin irritation, and some of them self-inflicted (e.g., bathing too frequently), seasonal allergies commonly afflict our pets and commonly manifest themselves as skin irritation. However, regardless of the cause of the skin irritation, the diagnostic protocol is very similar and is a combination of both circumstantial evidence (e.g., seasonal symptoms) and specific data (e.g., skin sampling such as a biopsy) collection.

Diagnosis of allergies can be difficult as the itchy, red, dry, flaky skin can be secondary to a variety of underlying causes and often complicated by self-induced trauma and subsequent infection of the skin - this is what ultimately leads to the 'hot spot' skin sores that you have described. At times, the diagnosis is achieved through exclusion of other common causes by the treatment of symptoms, such as antibiotics for a skin infection; however, if these confounding skin problems are successfully resolved yet the itchiness remains, allergies become the predominant likelihood (especially if there is a seasonal occurrence).

The only definitive diagnosis is through the collection and analysis of skin biopsies (a short procedure where a local anesthetic is used to harvest several very small samples of skin) and/or allergy testing. Allergy testing can be done through specialized blood tests or via intradermal skin testing, which is essentially the same procedure as used in people. This latter approach is preferred and still considered to provide better and more consistent results than the blood tests – especially in the hands of a veterinary dermatologist (yes! veterinarians that have specialized in disorders of the skin through additional residency training are available and can be invaluable for those animals with more complicated or ongoing skin problems). Food allergies may also manifest with similar symptoms, although bowel upset is also common. If food allergies are suspected, often the only way to determine this to be true is a trial hypoallergenic diet – many exist commercially but your veterinarian can also provide recipes for those wanting to try home cooking. Resolution of skin problems with reoccurrence when ‘re-challenged' with the old diet is fairly diagnostic for food allergies.

Further testing to better define the root cause would be an important step and may allow more specific treatment to be initiated, regardless of the eventual defined cause. For some skin ailments, such as allergies, there is no cure; however, knowing the cause can allow your veterinarian to tailor a control or preventative program to help minimize the symptoms and discomfort experience by your pet.

About Dr. Walt Ingwersen
Dr. Walt Ingwersen is Chief Veterinary Officer at PetCare Insurance Brokers Ltd. He is a 1982 graduate of the Ontario Veterinary College. Board certified in Internal Medicine, he has the distinction of being the first Canadian editor of the Journal of the American Animal Hospital Association, a position he currently holds.

Involved in many aspects of the national and international veterinary community, "Dr. Walt" is the recipient of the President's Award for outstanding contribution to the veterinary profession awarded by the Canadian Veterinary Medical Association (CVMA). He is also Chief Veterinary Officer and Chairman of the Veterinary Advisory Board at PetCare Insurance Brokers Ltd. – Canada's leading provider of insurance for dogs and cats.