white-catFeline Hyperthyroidism

By Dr. Mark Silberman, Southwest Animal Clinci, 4570 Bissonnet

Is your favorite feline friend getting old, skinny and grumpy? While this may appear to be “normal aging”, you may want to visit your veterinarian to have your cat’s thyroid function evaluated.

Hyperthyroidism is a common disorder affecting older cats. The average age at diagnosis is 13 years. Fortunately, malignancies of the thyroid gland are rare. In most cases of feline hyperthyroidism the thyroid gland is benignly enlarged, similar to goiter in people. The resulting symptoms are due to the excessive production of thyroid hormones in the body. Thyroid hormones, also called T3 and T4, are important in the maintenance of skin and haircoat and basal metabolic rate. Overproduction of these hormones results in an increase in the metabolic rate and an increase in the heart rate. This eventually leads to disabling weight loss, cardiac disease and high blood pressure.

Cat owners should visit their veterinarian if their pet is losing weight. This will occur in spite of a good appetite. Affected cats may appear agitated and vocalize more. They often drink more water and have an increased urine production resulting in larger clumps in the litter box. Vomiting may occur as well as a large volume of soft stool or diarrhea.

Diagnosis of hyperthyroidism is generally straightforward and can be accomplished by a simple blood test. A full blood panel including a T4 level will often be recommended as other diseases such as diabetes may have similar presenting symptoms. The veterinarian will also palpate the throat and neck region to see if an enlarged thyroid gland can be confirmed. In a normal cat, the lobes of the thyroid cannot be felt with ones fingers. Within 2-3 days the doctor will have the results. A significantly elevated T4 value confirms the diagnosis. Rarely, some cats with borderline values may require additional testing.