Hypothyroidism is the number one endocrine disease affecting dogs. Although it can occur in any dog, breeds most commonly affected include schnauzers, Scottish terriers, dachshunds, Doberman pinschers, golden retrievers and Labrador retrievers. The condition is quite rare in cats. 

Dogs suffering from hypothyroidism show a variety of clinical signs and vague symptoms. The most common signs include cold intolerance, lethargy, weight gain, and a variety of skin disorders. Dermal abnormalities such as hair loss, changes in coat color or quality, scaling and a predisposition to skin infections (pyodermas) are also noted. In fact the two most common reasons for recurring skin infections are hypothyroidism and allergies. Every chronically itchy dog should have a thyroid profile at least once before embarking on expensive allergy tests and treatment. Less frequently one might notice changes in mental awareness and reproductive failure.

Your veterinarian can test your dog's thyroid function with a simple blood test. This test measures the levels of active thyroid hormones being produced. If the concentrations are low, other tests may be needed to determine if the low levels are due to primary hypothyroidism or from the effect of other diseases or medications. In some cases a trial regimen of thyroid supplementation and observation of response may be needed to confirm the diagnose.

Luckily, hypothyroidism is an easily treated disease. Medication given once or twice daily often leads to resolution of most clinical signs. Usually treatment is for life.

Symptoms of overdosing are rapid weight loss, increased urination, increased drinking and nervousness. If any of these signs occur, you should call your veterinarian immediately. Usually your veterinarian will make an adjustment in the dose.

Resolution of symptoms may take several weeks. Usually within one to two weeks there will be an increase in activity. Skin disorders take longer. After two to three weeks it may look worse, as the old coat is shed. The skin takes about three months for a complete response and turnover. Mental awareness and reproductive disorders may take several months to bring about a complete resolution of the problems.

Every dog is individual, and the supplementation dose must be tailored. Four to eight weeks after starting hormone therapy a "post pill" T4 test is taken. This blood sample is drawn after an overnight fast, and then four to six hours after the supplement is given. Results should be in the normal range. If not, the dose can be adjusted in order to supply enough but not too much supplement. After adequate regulation is achieved, it is usually necessary to recheck the "post pill T4 test" every six months. 

Michael Shaff, V.M.D. owns and practices at The Animal Clinic of Woodmont, which is located at 8295 N. Pine Island Rd. in Tamarac, Fla. A University of Pennsylvania graduate, he is also a member of the South Florida Academy of Veterinary Medicine. He can be reached at (954) 726-3647 or by e-mail at acwoodmont@aol.com.

Article appears in the April/May 2001 issue of Pet Tribune, http://www.pettribune.com