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Red Bank Veterinary Hospital - Tinton Falls

Cat lying on an exam table next to a veterinarian


Feline hyperthyroidism is one of the most common diseases of older cats, usually due to enlargement of the thyroid gland. The veterinarians of Red Bank Veterinary Hospital have experience in diagnosing and treating this disease, as well as the effective treatment option radioactive iodine or I-131.

Diagnosing Hyperthyroidism

Symptoms of feline hyperthyroidism include weight loss, ravenous appetite, gastrointestinal signs, and hyperactivity. Excessive thyroid hormones affect every organ, leading to heart conditions and high blood pressure.

To diagnose feline hyperthyroidism, a thyroid hormone level blood test known as a T4 is performed. Some cats require additional blood testing or repeated thyroid levels.

Comprehensive Treatment

Therapies for hyperthyroidism include prescription diet, oral medication, removal of the thyroid gland, and radioactive iodine treatment.

  • Diet—An iodine-restricted prescription diet must be the only food given for effective reduction of the thyroid level. This treatment is not recommended in cats with pre-existing renal disease.

  • Oral medication—Methimazole reduces production of thyroid hormone when given twice daily in tablet form or compounded into a transdermal formulation. Gastrointestinal upset is common; less common side effects include liver toxicity, skin lesions, and decreased red blood cells and platelets. Side effects typically resolve when medication is stopped.

  • Surgery—Removal of the thyroid gland is rarely recommended. Although the surgery is fairly simple, anesthesia on an older hyperthyroid cat is considered high risk. Complications related to calcium regulation may also occur in the post-operative period.

  • Radioactive iodine—I-131 is an extremely effective therapy. In the body, iodine is naturally absorbed by the thyroid gland. Radioactive iodine is injected under the skin; the radioactivity is absorbed and destroys the abnormal thyroid cells, a permanent correction of hyperthyroidism. The patient is hospitalized for four to five days so levels of radioactivity can be measured. Once the level reaches an acceptable low range, the patient discharged.

If you are interested in radioactive iodine treatment for your cat, please speak with your primary care veterinarian or contact Red Bank Veterinary Hospitals Internal Medicine Department at (732) 747-3636.