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Thyroid Tumor Surgery in Cats

Reviewed by Dr. Peter Kintzer, DVM, DACVIM on Monday, October 19, 2015
Posted October 21, 2015 in Cat Surgery A-Z

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AJ Debiasse, a technician in Stroudsburg, PA, contributed to this article.

Did you know that cats can have a hyperactive thyroid gland? Also known as hyperthyroidism, it’s a fairly common condition in older cats. In fact, the vast majority of affected cats are older than 10 years of age. Most of the time, the reason is either a benign tumor or benign enlargement of the thyroid gland(s).

What is hyperthyroidism?
Hyperthyroidism is when thyroid glands work overtime and produce too much thyroid hormone. Because this hormone controls many organs, it can lead to multiple consequences:

Occasionally, a chubby couch potato kitty with gorgeous hair may turn into a skinny old cat with a rough hair coat, running around the house like a maniac.

How is hyperthyroidism diagnosed?
Since some of the signs of hyperthyroidism can be similar to other diseases, it’s important to perform a full work up. This starts with a thorough physical exam. A small nodule on the thyroid can often be felt by your veterinarian.

Blood work, including measurement of the thyroid hormone level, is the next logical step. The increased metabolic rate of hyperthyroidism can hide kidney issues and cause heart complications, so both should be monitored before and after treatment has been started. This requires blood work, X-rays and ultrasound.

How is hyperthyroidism treated?
There are several treatment options:

  • Methimazole is a medication that fights hyperthyroidism. It is usually given by mouth, every single day. Methimazole can also be compounded into a cream which is applied to the skin or the ear daily (transdermal application).This is a life-long treatment.
  • I know about at least one special diet that is very low in iodine, and was introduced a few years ago. If your veterinarian recommends this option, this is the only food your cat should eat for good results.
  • Veterinary endocrinologists consider IV radioactive iodine treatment as the gold standard for hyperthyroidism.
  • Surgery to remove the tumor is an option, although it is less and less common. It’s a delicate surgery but in good hands, it is highly successful.

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Dr. Phil Zeltzman is a board-certified veterinary surgeon and author. His traveling practice takes him all over Eastern Pennsylvania and Western New Jersey. You can visit his website at, and follow him at