Treatment options for hyperthyroidism

Hyperthyroidism can either be cured with radioactive iodine, or the symptoms of the disease can be managed for the rest of the cat’s life with a medication or a prescription diet.

Radioactive iodine is widely accepted as the “gold standard” treatment for this disease and is the treatment method employed for human patients with hyperthyroidism.

Radioactive iodine is administered as an injection under the skin. The iodine, which is required for the production of thyroid hormone, is quickly absorbed into the bloodstream and taken up by the thyroid gland. The emitted radiation selectively kills tumor cells that overproduce thyroid hormone, leaving normal thyroid tissue and other organs unharmed.

Radioactive iodine can only be administered at specially licensed facilities, and cats must remain hospitalized until their radiation levels fall to acceptable limits for their release (depending on state regulations, hospitalization time will vary from 2-5 days).  After the cat is released, the family must follow some common sense precautionary measures at home for 2-4 weeks.

Methimazole is a drug that interrupts the production of T4 hormone by the thyroid tumor cells.

Disadvantages of methimazole include:

• The thyroid tumor continues to grow unchecked; over time, the tumor can develop into an aggressive growth that is difficult to control by any means
• The drug must be given twice a day, every day, for the rest of the cat’s life
• Drug side effects occur in up to 1/3 of cats – these include loss of appetite, vomiting, inflammation of the liver, anemia, low white blood cell counts, and irritation of the facial skin
• Blood panels must be checked every 6-12 months for the rest of the cat’s life
• Long term, methimazole is the most expensive treatment option due to the costs associated with the drug itself and the need for repeated lab work

An extremely low iodine prescription diet is available to manage symptoms of hyperthyroidism by decreasing the amount of thyroid hormone the tumor cells can produce.

Disadvantages of an iodine-restricted diet include:

• The diet must be fed exclusively for the rest of the cat’s life. Absolutely no other cat foods, table foods, or treats can be given if the diet is to be effective
• The food is not highly palatable; many cats refuse to eat it
• It may not be the best diet for cats with other medical conditions, such as chronic kidney disease, allergies, or intestinal disease

Similar to methimazole, the thyroid tumor continues to grow unchecked and may eventually grow large enough or transform to a malignant growth that is difficult to control by any method.