Treatment of Hyperthyroidism in Cats

There are several options for treating hyperthyroidism in cats.  Since each treatment has its own set of benefits and drawbacks, it is vital to match the treatment to the individual cat.  Please discuss these options with your veterinarian before deciding on a course of therapy. 

1)  Thyroidectomy:  Surgical removal of the diseased tissue was the treatment of choice for cats with hyperthyroidism until radioiodine was discovered.  The procedure requires a skilled surgeon to avoid damaging the parathyroid gland which rests adjacent to the thyroid gland.  It is also very difficult to find and remove ectopic tissue (tissue outside the normal gland) that is often found inside the chest cavity.   

2)  Radioiodine:  Radioiodine or I-131 is injected into the cat’s blood stream, absorbed by the thyroid glands and then destroys the thyroid tissue.  The advantage of this procedure is that it gets the ectopic tissue as well as the thyroid glands.  It does not require anesthesia which is another benefit.  Thyroid function usually returns to normal within 30 days.  Before using this treatment option, make sure the cat has good kidney function.  As I discussed in the prior posts, hyperthyroidism may mask kidney disease.  More information is available at

3)  Anti-thyroid Drug Therapy:  Methimazole which goes by the trade name of Tapazole is an anti-thyroid drug commonly used in veterinary medicine.  It is important to note that this medicine does not cure hyperthyroidism.  It just blocks the synthesis of thyroid hormone.  The drug is dosed in one of two ways, oral or transdermal in cats who are difficult to pill.  Unfortunately, there may be many unwanted effects associated with methimazole including hepatopathy (liver disease), blood disorders and auto immune disease.  I had one patient develop dermatitis on his face.  The poor guy rubbed his cheek into a bloody mess.  Most of these problems occur within the first three months of treatment.  It is important to perform blood work every two to three weeks in newly treated cats to catch these problems early. 

4)  Hill’s YD: YD is an iodine deficient diet that is the newest treatment for hyperthyroidism.  Without enough iodine in the diet, the thyroid gland cannot make as much thyroid hormone and blood levels fall.  According to Hill’s, thyroid health will be restored in three weeks as long as no other foods are given.  I know Hill’s to be a wonderfully responsible firm.  They do a great deal to assist us as veterinarians in caring for animals.  That said, this new diet leaves me with a few questions.  Since cats are obligate carnivores meaning they must eat animal protein in order to maintain good health, I am concerned about this diet.  Most of the protein, especially in the dry form, is from plants.  In addition, I am concerned about the carbohydrate level which I worry could potentially lead to diabetes mellitus and/or pancreatitis. Here is the company’s website for more information,  I hope Hill’s is able to satisfactorily answer these questions as it is exciting to have food as an option for this condition. 

Published by kristennelsondvm

Dr. Kristen Nelson grew up on a farm in Watertown, Minn., where she developed a deep love for animals of all kinds. She received a Doctor of Veterinary Medicine degree from the University of Minnesota, College of Veterinary Medicine. Kris then completed a small-animal internship at the prestigious Animal Medical Center in New York City. In addition to writing and speaking, she cares for small and exotic animals in Scottsdale, Az. Dr. Nelson is widely quoted in the media. Her credits include Ladies’ Home Journal, USA TODAY, the Los Angeles Times and numerous radio and television interviews. Dr. Nelson has written two books, Coated With Fur: A Vet’s Life and Coated With Fur: A Blind Cat’s Love. Kris and her husband Steve share their home with rescued cats, birds and a dog.

Leave a comment

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.