Skinny Old Cats

Pet obesity is a large problem in the U.S. The opposite can often be true for our geriatric cats. It’s common to see a cat who is in her early to mid teens that has lost weight over the past couple of years and is now thin. Her appetite is great and she is very active. Her hair coat isn’t as soft and sleek as it used to be and she does throw up once in awhile. When we listen through a stethoscope, her heart is racing even while she is calm.

This collection of signs suggests a disease called hyperthyroidism or overactive thyroid gland. The thyroid is a small gland located in the neck. It secretes hormones to help keep the body running smoothly. The hormone responsible for signs of hyperthyroidism is called thyroxine. One of its major functions is to regulate metabolism. Higher levels of thyroxine increase or speed up metabolism.

Hyperthyroid cats have small tumors in their thyroid glands. These tumors don’t listen to the normal signals that tell the thyroid to turn thyroxine secretion on or off. They are always on and produce more thyroxine than is normally required. The cat’s metabolism is revved up so the heart rate is rapid, they are very active and they can not keep weight on. The vomiting may be from intermittent nausea. Untreated, hyperthyroidism can lead to heart damage, increasing digestive upset, uncontrolled weight loss and death.

A diagnosis of hyperthyroidism is based on blood testing. Since the cats affected by hyperthyroidism are geriatric, and at risk for other chronic health problems, it is important to screen for other diseases that can result in weight loss- kidney disease, liver disease, diabetes mellitus, and others. The presence of other diseases may make treating hyperthyroidism complicated.

Treatment usually starts with a medication called methimazole. It damages the thyroid’s ability to produce thyroxine and can reduce levels to normal. It is given daily to maintain effect. It can sometimes cause side effects such as vomiting and severe facial itching. If it is not tolerated, another treatment should be pursued. Regular monitoring of blood levels of thyroxine are necessary.

Cats who do not tolerate methimazole or are very difficult to medicate may be treated with radioactive iodine or I 131. The thyroid uses iodine to make thyroxine. When I 131 is administered, it is taken up by the thyroid tissue. The radiation destroys the tissue and its ability to make excessive thyroxine. It is a very safe and effective treatment. Treated cats do not require further medication and one follow up thyroxine level is usually sufficient. I 131 treatment does require your pet to spend a few days at a hospital that is specially licensed to handle I 131. It also requires a significant up front cost.

Surgery can also be performed to remove the affected thyroid tissue. Patients regain normal thyroid function and don’t require medication. Disadvantages of surgery are risks of postoperative pain and infection, inadvertent injury to the parathyroid glands leading to potentially life threatening hypocalcemia, and growth of a new tumor in remaining thyroid tissue.

Older cats who are losing weight may be trying to tell us something. Getting them checked for hyperthyroidism and other geriatric diseases can help maintain healthier golden years.