What is hyperthyroidism?

Hyperthyroidism is the overproduction of thyroid hormone by the thyroid glands.  Hyperthyroidism occurs most commonly in older cats and is rare in dogs.  The average age of cats with hyperthyroidism is 13 years of age; only about 5% of hyperthyroid cats are younger than 10 years of age.  There are 2 thyroid glands located in the neck.  One or both of the glands can enlarge and overproduce thyroid hormone.  Involvement of both glands is more common than involvement of one gland.  Thyroid hormone affects the function of most organs in the body, so the signs of hyperthyroidism are quite variable.

Signs of hyperthyroidism can include:

• Weight loss

• Increase appetite

• Increased activity and restlessness

• Aggressive or “cranky” behavior

• A poor hair coat

• A fast heart rate

• Increased water drinking

• Increased urination

• Periodic vomiting

• Increased amount of stool or diarrhea

• Occasionally difficulty breathing

Diagnosing Thyroid Disease:

Luckily, thyroid disease can be diagnosed by a simple, inexpensive blood test.  Because kidney, liver and certain cancers can have similar signs to hyperthyroidism, a complete blood chemistry analysis of all organs on cats should be done.  The values within this panel that detect the disease are T-4, Free T-4 and T-3.  These tests measure the amount of thyroid hormones present in the blood.

Can it be prevented?

There are no preventative measures to adopt, but middle-aged and geriatric cats should all receive a complete physical by a veterinarian every 6-12 months.  Special attention should be given to thyroid enlargement and the typical clinical signs of hyperthyroidism.

There are three types of treatment for hyperthyroidism:

• Lifelong oral anti-thyroid medications

• Surgical removal of affected thyroid glands

• Treatment with radioactive iodine

• All three treatments will reduce thyroid hormone levels and the signs of hyperthyroidism.