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Allergic Skin Diseases in Dogs

November 20, 2017

Skin and haircoat changes may occur for a number of different reasons including:
  • Environmental allergies
  • Food allergies
  • Contact or irritant skin disease
  • Breed-related and genetic disorders
  • Scaling disorders
  • Hormonal conditions
  • Nutritional disease
  • Parasites
  • Immune-mediated skin disorders. 
Diagnostic tools are used to rule out some of these other conditions listed above, since skin disorders can look alike on visual inspection.
 
Skin allergy is a condition that affects 3.3 to 27 per cent of the canine population, depending upon which report is being referred to. The veterinarian will rule out basic categories of skin problems via magnified careful visual exam, flea combing, skin scraping, and stained skin surface samples to check for secondary infection with bacteria and yeast; sometimes cultures for ringworm (fungal) and bacteria will be done. Basic blood and urine tests may be done assess internal health before considering various treatments.
 

Allergic Skin Disease

The age of onset of allergic skin disease is usually between six months and three years of age, though skin disease can start at any age. At first, the allergy may surface during a particular season, but as the patient gets older, the signs of allergy can potentially worsen and last all year long, or there may never be seasonal pattern at all.
 
A prominent sign is itchiness (pruritus) so the pet may:
  • Rub the face around eyes, ears, and muzzle;  
  • Experience chronic recurrent ear infections;
  • Bite, chew or lick paws, or at the back legs where they join the body (groin) and/or in the armpit (axilla);
  • Scratching may involve the whole body.
Signs may be complicated by secondary infection with bacteria or colonization by yeast that take advantage of the damaged skin barrier. If left untreated, this can lead to serious secondary infections. An infection can make itching even more severe, as well as complicating the treatment of this disease.
 
Your veterinarian will carry out thorough history taking and perform a physical examination of the pet. A skin allergy test or blood allergy panel also may be recommended to help determine what it is that your dog is allergic to, and to help formulate allergy therapy (called immunotherapy).
 

Skin Irritations Could be Due to a Food allergy

Food allergy and intolerance in dogs is thought to account for approximately five to 22 percent of all skin cases seen in clinical practice. The most common triggers are beef, dairy products, chicken, wheat, eggs, corn and soy. However, dogs can be allergic to foods other than these and to more than one kind of trigger.
 
To determine if a dog has food sensitivity, the veterinarian may elect to place the dog on an elimination test diet. Novel diet trials remain a reliable and accurate method for diagnosis of food allergies.  Elimination diets are very simple—usually one novel protein source one easily digested novel carbohydrate will be prescribed, along with vitamins and minerals and fibre to balance the test diet. If the dog improves on this limited diet after 6 to 8 weeks, suspected triggers may be added back one at a time to see if signs return.  Once a diagnosis of food sensitivity has been confirmed, the dog can then be put on a balanced diet without that trigger.
 
If, on the other hand, testing proves that the dog does not to have a food allergy, there are many other possible environmental reasons for allergic skin disease in dogs. Your veterinarian will do additional tests or refer to a dermatologist to try to determine a cause and treat accordingly.
 

The Importance of Testing

A common complaint of owners is the extensive and costly testing sometimes required to narrow down the source of the skin issues. In reality, the investment is well worth it, since ongoing therapies required to treat general signs of an undiagnosed chronic skin condition can run into the thousands of dollars over a lifetime of the pet, and may not hit the mark.
 
In contrast, specific diagnosis will allow the veterinarian to narrow the scope of therapies to ensure money is well spent on only the required medication that will have positive effect, improve the chances of controlling the problem, and thus improving the health and welfare of the pet.
 

Helpful Tips to Control or Cure

Not all skin allergy problems are fully controlled or cured. 
 
Avoidance is the best strategy with food sensitivity, but is not always possible if there are other triggers.  There are many effective control strategies. For best control, more than one treatment is needed (multimodal).
 
Essential fatty acids have been shown to be effective in somewhat reducing the level of itchiness, for at least some dogs. Fish oil preparations may be added to the diet or provided as a supplement to normalize skin lipids and enhance coat gloss. Beneficial effects of fatty acid supplementation may take 8 weeks or more to be visible.
 
Antihistamines have proven to be effective in controlling allergic symptoms in people however this has not proven to be the case in many animal species. In dogs, some antihistamines are more effective than others, and itchiness may not resolve with antihistamines. Your veterinarian should be consulted regarding which antihistamine is most effective for your dog. Sometimes a trial of a few different types is required before the optimal action and dose is achieved.
 
Steroids, including prednisone/prednisolone or dexamethasone can be effective for the control of itching in healthy dogs. Unfortunately there are side effects sometimes associated with use, but lower doses may be used safely in an otherwise healthy dog. The lowest possible doses are used to minimize risk of side effects, and your veterinarian will discuss side effects if it is an elected therapy. Other newer treatments have somewhat replaced these old stand-bys. Steroids are frequently combined with antihistamines so that the dose can be kept low, and in many cases, every other day treatment is done to minimize the impact on the metabolism. If treatment with prednisone and other steroids is terminated abruptly, these animals become particularly vulnerable to stress. For this reason, withdrawal from treatment is usually done gradually, by reducing the dose as instructed by your vet in order to allow the body to adjust. 
 
Apoquel® (oclacitinib) is a medicine that works to counteract pruritus and inflammation-producing cytokines that are chemicals released during allergy. It is prescribed for dogs over one year of age and in good health, with few side effects or drug interactions reported. 
 
Immunotherapy Injections are also known as hyposensitization, desensitization, or allergy shots. This is a safe, reliable and fairly effective modality, though costly. Immunotherapy involves testing the dog to see what the pet is allergic to.  With repeated injections, the patient eventually becomes desensitised to the offending allergens and the injections can be discontinued.
 
Cytopoint® is a newer injection given under the skin for atopic dogs that works by adjusting the availability of certain metabolic products (interleukins) using specific manufactured monoclonal antibodies. It can be used in dogs of all ages, and with other health problems with no known drug interactions since it is not a drug per se. Only rare side effects have been reported.
 
Several topical treatments assist in reduction of the levels of itchiness and help to restore a normal skin barrier, though they do not resolve the underlying sensitivity. Topical creams and ointments, pour-on products and medicated baths may be prescribed to help restore the normal skin barrier. Therapeutic shampoos, especially those containing oatmeal, or having antifungal or antibacterial action are particularly effective, though bathing can be labour-intensive.
 
With proper ongoing care, many pets can have an excellent quality of life. Multimodal therapy (more than one component) is often key to good control, and with additional new therapy options available in recent years, your veterinary health care team can provide sensitive pets with a good quality of life!
 
Dr. Kathleen Cavanagh, Consulting Online Editor CVMA
BSc DVM MET
 
Dr. Stephen Waisglass, Dermatology Specialist Consultant
DVM CertSAD, DACVD