Feline hyperthyroidism, is a common disorder in middle-aged and older cats. It occurs in about 10 percent of cats over 10 years of age. Hyperthyroidism is a disease caused by an overactive thyroid gland that secretes excess thyroid hormone. Cats typically have two thyroid glands, one gland on each side of the neck. One or both glands may be affected. The excess thyroid hormone causes an overactive metabolism that stresses the heart, digestive tract, and many other organ systems.
If your cat is diagnosed with hyperthyroidism, they should receive some form of treatment to control the symptoms. Many cats that are diagnosed early can be treated successfully. When hyperthyroidism goes untreated, clinical signs will progress leading to marked weight loss and serious complications due to damage to the cat's heart, kidneys, and other organ systems.
Sad Cat — Emergency Animal Services in Bonita Springs, FL


If you see any of the following behaviors or problems in your cat, it possible that your cat has hyperthyroidism:
  • weight loss despite a normal or increased appetite
  • increased drinking or thirst
  • increased urination
  • defecation and urination outside of the litter box
  • increased vocalization
  • restlessness, increased activity
  • vomiting
  • diarrhea
  • rarely, lethargy and a lack of appetite
  • poor hair coat, unkempt fur


Twice yearly examinations of your cat may allow early detection of hyperthyroidism, as well as other age related diseases. During the physical examination, your veterinarian may discover increased heart and respiratory rates, hypertension, a palpable thyroid gland, and loss of muscle mass. Routine screening of laboratory tests and blood pressure may detect abnormalities before symptoms are advanced. Blood testing can reveal elevation of thyroid hormones to establish a diagnosis of hyperthyroidism. Occasionally, additional diagnostics may be required to confirm the diagnosis. Because hyperthyroidism can occur along with other medical conditions, and it affects other organs, a comprehensive screening of your cat's heart, kidneys, and other organ systems is imperative.
Cat Getting a Injection — Emergency Animal Services in Bonita Springs, FL


If your cat is diagnosed with hyperthyroidism, your veterinarian will discuss various treatment options. Three common treatments for feline hyperthyroidism are available and each has advantages and disadvantages. The choice can depend on factors such as the cat's age, other disease conditions, treatment cost, and our professional recommendation.
Radioiodine therapy – commonly called I-131. This is considered the gold standard for treatment of hyperthyroidism. This treatment consists of administering a small dose of radioactive iodine which only overactive thyroid tissue will absorb. The radiation destroys the abnormal cells while the normal thyroid tissue continues to function. Even though this radiation exposure carries minimal risks for you and your cat, special facilities are required for treatment, and specific isolation protocols need to be followed after discharge. The advantages of I-131 treatment are that it offers an actual cure and there is no anesthesia, surgery, or risk of drug reaction. Southwest Florida Veterinary Specialists & 24-Hour Emergency Hospital is one of a few facilities that provide this therapy as a specialized and licensed treatment center.
Thyroidectomy – a surgical technique which removes all or part of the thyroid gland. The advantage of surgery is that it can be curative and eliminate the need for life-long medication. The disadvantages of surgery are that your cat requires general anesthesia and not all cats are good surgical candidates. Additionally, varying complications of surgery may occur including damage to nerves and blood vessels of the neck, damage to the parathyroid gland function, and recurrence of hyperthyroidism as unrecognized tissue can remain even with the best surgical techniques.
Medical therapy – anti-thyroid medications will control the disease and block the excess production of the thyroid hormone; however because this medication does not cure the disease, your cat must take it for its entire life. Your cat may also receive the drug as a short-term measure, prior to surgery or anesthesia, or if radioiodine therapy is not available right away. Advantages of medical therapy- a low initial cost, readily available treatment, and no hospitalization. Disadvantages include lifelong medication, adverse drug reactions, and long-term costs of treatment.
Advantages Include:
  • 98%+ success rate.
  • No lifetime medication regimen.
  • No surgery or anesthesia.
  • No effect on normal thyroid tissue or the nearby parathyroid tissue.
  • The total cost of I-131 is less than other treatment methods over the lifetime of the cat.