2001-Fri Jan 18 06:53:57 EST 2019
Vetstreet. All rights reserved. Powered by Brightspot.
Vetstreet does not provide medical advice, diagnosis, or treatment. See Additional Information ›
Feline hyperthyroidism is the most common glandular disorder of cats older than 8 years. The disorder is usually caused by a benign tumor in one or both of the thyroid glands, which are located on either side of the neck. These tumors cause the thyroid glands to over-produce thyroid hormones. In rare cases (1% to 2%), the tumors may be cancerous.
Thyroid hormones are important for regulating metabolism. When a cat has abnormally high levels of circulating thyroid hormones, the cat’s metabolic rate increases, leading to secondary problems associated with increased blood pressure. High blood pressure can damage other organs, such as the heart, kidneys, liver, and eyes.
Cats with hyperthyroidism may show any or all of the following signs:
Diagnosis of feline hyperthyroidism begins with a medical history and physical examination. In some cases, the veterinarian may be able to feel enlarged thyroid glands on either side of the cat’s neck. If hyperthyroidism is suspected, the veterinarian will recommend blood tests to confirm the diagnosis.
A baseline thyroid level test is a simple blood test to determine the level of thyroid hormone (T4) in the blood. It is a good screening test for cats that have signs associated with hyperthyroidism. A high total T4 level confirms the diagnosis of hyperthyroidism.
Occasionally, cats with signs of hyperthyroidism may have normal or borderline results on the baseline thyroid level test. It’s possible for other illnesses to lower the T4 level. In this case, your veterinarian may recommend a thyroid profile test.
This blood test usually measures a variety of hormones, including T3 (another thyroid hormone), TSH (thyroid stimulating hormone), and free T4 (the amount of T4 that is not bound to protein in the blood). The free T4 level is not influenced as readily by other illnesses and generally remains high in cats that are hyperthyroid. Compared with the baseline thyroid level test, the profile may provide a more accurate assessment of thyroid function. Because this test is more expensive, veterinarians sometimes start with the simple thyroid level test.
Your veterinarian may also suggest a T3 suppression test. With this test, a baseline blood sample is taken, then the cat is administered a T3 pill over the course of 3 days, followed by another blood test. The result may help diagnose cases of borderline hyperthyroidism.
There are a number of options for treating hyperthyroidism.
A common medical treatment for hyperthyroid cats is administration of an oral pill called methimazole. The pill must be given daily—usually twice a day—for the life of the cat. Periodic testing of the baseline T4 level is recommended, as dosage adjustments are sometimes required for continued management of the condition. Most cats tolerate methimazole very well, but side effects may include vomiting and facial itching.
A second and more permanent solution is treatment with radioactive iodine. When radioactive iodine is administered, it destroys the cat’s thyroid tissue. While the procedure is relatively safe, the cat must remain at a special facility during treatment, which may require 7 days or more of hospitalization. Treatment with radioactive iodine usually cures the thyroid condition, so no pills are needed.
Another treatment option is surgical removal of the thyroid glands. If all of the abnormal tissue is removed, this treatment can cure hyperthyroidism. However, there may be anesthesia risks with older cats, and the surgery may result in complications.
Untreated hyperthyroidism can lead to heart failure, sudden blindness from high blood pressure, chronic vomiting and diarrhea, and death. Thyroid testing can help diagnose feline hyperthyroidism so that proper treatment can be initiated and the effects of the disease may be mitigated.
This article has been reviewed by a Veterinarian.
Like this article? Have a point of view to share? Let us know!
Bartonella is a type bacteria that can be transmitted to cats, dogs and humans from exposure to infected fleas and…
Want to give your pup yummy, low-calorie treats? We’ve got the skinny on which foods are OK to feed him.
Not sure about food puzzles? Our veterinarian reveals why the payoff for your pet is well worth any extra work.
With these simple dental care tips, you can help keep your canine’s adorable smile shiny and healthy for life.
The friendly and inquisitive LaPerm has an easy-care coat that comes in a variety of colors and patterns.
Check out our collection of more than 250 videos about pet training, animal behavior, dog and cat breeds and more.
Wonder which dog or cat best fits your lifestyle? Our new tool will narrow down more than 300 breeds for you.
Thank you for subscribing.