Hypothyroidism

Hypothyroidism is a commonly occurring disease in dogs, but is found rarely in cats. It is the condition that occurs when not enough thyroid hormone is produced. The production of thyroid hormone is influenced by the pituitary gland, the hypothalamus, and the thyroid gland. More than 95% of all cases of hypothyroidism occur as a result of destruction of the thyroid gland by immune mediated disorders or thyroid gland atrophy with fat infiltration.

The thyroid gland has a number of different functions, but it is most well known for its role in regulating metabolism. Hypothyroidism causes a wide variety of symptoms including weight gain/obesity, hair loss and skin problems. The disorder usually affects mid to large size breeds of dogs between the ages of 4 to 10 years.  Breeds that appear to be predisposed to developing the condition include Golden Retrievers and Rottweillers.  It does not appear to occur in one sex more than the other, but spayed females appear to develop it more often than intact females.

Diagnosis

Baseline T4 Test: The most common test performed to diagnose hypotheyroidism is the baseline T4 test. A blood sample is drawn and tested by radioimmunoassay to determine the level of T4 thyroid hormone in the bloodstream. The T4 hormone is produced only in the thyroid gland and dogs with a failure of the thyroid gland will have a lowered level of this hormone. However, there are other conditions that can cause a lowering of T4 so if this screening test is positive for hypothyroidism a TSH (Thyroid Stimulating Hormone) test is often done to confirm the diagnosis.

Treatment

Treatment for hypothyroidism consists of putting the dog on a daily dose of a synthetic thyroid hormone medication called levothyroxine (Thyro-tab). The dose and frequency of administration of this drug varies depending on the severity of the disease and the individual response of the pet to the drug. The pet is usually placed on a standard dose for his weight and then blood samples are drawn periodically to check his response and then the dose is adjusted accordingly. Once drug therapy has been started, the dog will need to be on this treatment for the rest of his life. Usually after the treatment is started, the majority of symptoms resolve.

At Mission Veterinary Hospital we like to be sure that we are treating your pet to the best of our ability. We recommend a complimentary weigh-in every three months, annual blood tests to monitor T4 levels and a general health examination done annually once the condition is under control.