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Thyroid Gland

All Creatures Animal Clinic, Ltd.

Mark Hale, DVM

1661 E. Mt. Gilead Rd.

Bolivar, Missouri  65613



The Thyroid Gland of Dogs and Cats


            Is your dog losing hair excessively or is your older cat eating well but still losing weight?  If so, then thyroid conditions may be a possible explanation.

            The thyroid gland in dogs and cats lies near the larynx adjacent to the trachea.  The hormones secreted by these glands are the only iodinated (‘with iodine') organic compounds in the body.  The level of thyroid hormone in the bloodstream is regulated by the pituitary gland.

            In dogs, the most common thyroid disorder is a low thyroid hormone level, or hypothyroidism.  Over 95% of hypothyroidism in dogs is due to destruction of the thyroid gland itself.  This disease is most common in middle-aged mid-to-large size breeds.  Breeds most commonly affected include Miniature Schnauzer, Dachshund, Cocker Spaniel and Golden Retriever.  However, it can happen in any breed of any age.  I even documented it once in a tiny three-month old Pomeranian (which luckily responded great to treatment). 

Clinical signs most common with hypothyroidism include hair loss, dull dry hair coat, skin infections, mental dullness, slow heart rate, anemia, obesity and lethargy.  As you can see, it can present with a variety of signs (and those listed are only the most common ones) so diagnosis is not always easy.  Blood tests are required to confirm the diagnosis, and other tests are usually needed to rule-out other possibilities for the clinical signs. 

Treatment of the condition involves thyroid replacement usually given twice daily.  A response is usually seen in one to two months' time or less.  Secondary skin infections, ear infections, and obesity may require other concurrent treatments.  With few exceptions, replacement hormone therapy is necessary for the remainder of the dog's life.  Fortunately, this drug is very inexpensive.  Periodic monitoring of the blood hormone levels is necessary to determine the correct dosage for each individual.

In cats, we usually see the opposite situation compared to dogs.  Hyperthyroidism or an excess thyroid hormone level occurs most often in middle-aged to old cats and causes signs due to the increased metabolic rate.  A benign enlargement of the gland is most common, but cancerous thyroid tumors can also occur.

Symptoms seen in these cats can include weight loss, increased thirst and urination, increased appetite, vomiting, diarrhea, heart murmurs, and heart failure.  Some of these cats I have seen have kidney failure at the same time which can make treatment more complicated.  Blood tests to determine the thyroid level as well as to check other organ functions are necessary for diagnosis.

Treatment usually consists of giving an anti-thyroid drug daily, either orally or applied topically inside the ear.  This treatment will be continued for life.  Adjustments may have to be made in the dosage based on follow-up blood tests.  Cats with hyperthyroidism can often regain a good quality of life for several years.

If your cat or dog is showing symptoms such as these, please discuss it with Dr. Hale.  The earlier these conditions are treated, the greater the chances are of a good response.