Hyperthyroidism is a commonly diagnosed condition in older cats. It is caused by a tumor that produces too much thyroid hormone. If left untreated the disease is usually fatal. Feline Hyperthyroidism may be treated with medicine, surgery, or radioactive iodine:
There are three main ways to treat feline hyperthyroidism.
Drugs: Your cat can take a daily dose of methimazole – Tapazole®. Methimazole is given one to three times daily and must be continued life long. It takes several weeks for methimazole to reduce blood thyroid hormone levels to normal. If methimazole is discontinued, thyroid hormone levels will return to high levels over a few weeks.
Methimazole may be used to reduce thyroid hormone levels to normal before surgically removing the thyroid gland(s). This drug is a life-long treatment and does not cure your cat’s hyperthyroid condition. The difficulties associated with giving pills to cats often causes stress to both you and your cat. Tapazole may have side affects that effect your cats liver and blood system. The amount of the drug must be adjusted often, based on regular blood tests. Methimazole may produce side effects in cats including depression, vomiting and lack of appetite. The cost of this treatment and tests is usually over $800 per year!
Surgery: Surgical therapy for feline hyperthyroidism requires anesthesia. Often the first surgery does not remove all of the tumor and another surgery may needed.
In some cases too much of the thyroid gland is removed resulting in a deficiency of parathyroid hormone in your cat, know as hypothyroidism. This may require your cat to take thyroid pills. Surgery may remove all of the affected thyroid tissue that is causing your cats hyperthyroidism. Occasionally complications may develop including damage to the parathyroid glands, which are closely attached to the thyroid gland, damage to nerves close to the thyroid gland or damage to the voice box. Parathyroid gland damage causes low blood calcium that may cause seizures. Low blood calcium is treated with calcium or vitamin D. Nerve damage causes abnormal size of the pupils of the eyes and droopy eyelids. Damage to the voice box causes a change in voice.
Some cats will remain hyperthyroid after surgical removal of the thyroid glands. These cats have thyroid cells in abnormal locations, including inside the chest cavity where surgical removal is difficult. This extra thyroid tissue is called ectopic thyroid. If you and your veterinarian decide that surgery is the best treatment option for your cat, a nuclear medicine scan could be performed at a specialty veterinary practice before surgery to see if your cat has ectopic thyroid tissue. If ectopic thyroid tissue is seen on the nuclear medicine scan, then a different treatment, either methimazole or radioactive thyroid treatment should be selected. Cats that have had surgery may have recurrence of hyperthyroidism. Cost of surgery can vary depending on your location, but multiple surgeries can add up over $1000 very quickly.
Radioactive Iodine (RAI) therapy: This cure for feline hyperthyroidism is very effective. There are few side effects to RAI therapy. I131 therapy is a one-time treatment. It is effective in over 95% of cats with hyperthyroidism. I131 therapy does not require your cat to take any pills or be given anesthesia. Your cat will receive one small injection under the skin. The cost of radioactive iodine therapy ranges from $800-$1200. For more information on RAI therapy read the post: Feline RAI (131) Treatment