Hyperthyroidism or an overactive thyroid is a common disease in geriatric cats. As some cats age, they develop one or more nodules on their thyroid gland. Though they tend to be benign in nature, they will almost always secrete thyroid hormone. When a cat has too much thyroid hormone the most common signs you will see are:
- Weight loss with a ravenous appetite
- An increased thirst and urination
- Vomiting
- Diarrhea
- Unusual behavior (occasionally)
Hyperthyroidism can be tested by performing a blood test.
If your cat has hyperthyroidism, we recommend treatment to decrease the effects of an overactive thyroid. When a cat has too much thyroid hormone in their body:
- It can be toxic to many organ systems, including the heart and liver
- It can cause the heart to become enlarged and not able to do its job as effectively
- It can increase a cat’s blood pressure
- The liver will often be damaged, and there will be noticeable changes in the liver enzymes
Unfortunately, the changes in the heart are permanent. However, the good news is that the damage to the liver can be reversed.
There are three treatment options to help control hyperthyroidism.
1. Methimazole (Oral or topical medication): This is not a permanent treatment for hyperthyroidism.
- For most cats, medication must be given twice a day for 3-4 weeks and thyroid levels will be checked often after consistent use.
- The three methods for giving Methimazole are:
- Pill form
- Liquid suspension
- oransdermal gel: Absorbed through the skin; applied to the inner surface of the ears, alternating between ears.
The oral or topical medication is a good option meant to help control the thyroid levels in your cat.
2. Radioactive Iodine ( I131 ): This is a permanent treatment for hyperthyroidism.
- Before beginning this treatment, your cat must do a trial with oral or topical medication prior to radioactive iodine. If your cat’s kidneys handle the thyroid being controlled, then it is eligible for treatment. Your cat is given Radioactive Iodine, which targets the overactive part of the thyroid, leaving behind the normal thyroid. Treatment takes approximately one week after which your cat may return home when he is no longer radioactive and a danger to you
3. Thyroidectomy or thyroid surgery: This is another permanent treatment for hyperthyroidism.
- As with radioactive iodine your cat must do a trial with oral or topical medication prior to surgery. If your cat’s kidneys handle the thyroid being controlled, then surgery may be an option for you. The thyroid glands are located in the neck. Your cat would have an incision over the trachea (windpipe) just below the throat to remove the overactive part of the thyroid.
In some cases, if the kidneys have a hard time functioning after the thyroid is under control, the treatments for a more permanent change such as Radioactive Iodine or Thyroidectomy may not be the best options for your cat.
If you are concerned that your cat may have hyperthyroidism, schedule an appointment for an exam and bloodwork. The best treatment option depends on your cat as well as your lifestyle. Our veterinarians will discuss the treatment options, side effects, and potential risks with you to help determine which option is best for your cat.
HYPERTHYROIDISM IN CATS
By Dr. Jennifer Tutko, DVM
APRIL, 2011
