Hyperthyroidism is Senior Cats

The cat nervously paces the exam table while I talk with the owner.

The owner explains that her cat has a great appetite but is still losing weight.

“Perhaps she has worms,” offers the owner.

I examine the cat and note that she is very thin, her heart is racing along at about 200 beats per minute, and that she has a bump where her thyroid gland is located.

I explain to the owner that the most likely diagnosis is hyperthyroidism.

Hyperthyroidism is usually the result of a benign growth on the thyroid. The growth puts out excess thyroid hormone, and ramps up the cat’s metabolism.  So despite a great appetite, the cat’s body burns off the excess energy quickly.

Not all cats show the same signs with hyperthyroidism.  Some show decreased appetite, vomiting or diarrhea. Laboratory tests can confirm the diagnosis.

Treatment options consist of injection of radioactive iodine (done at a specialty practice), thyroidectomy (surgical removal of the thyroid), or medicine given twice daily (methimazole).

The best treatment for hyperthyroidism is the radioactive iodine treatment. This treatment permanently removes the excess thyroid tissue and creates a normal to low thyroid state for cats.  It is costly and the cat must remain at the specialty practice for several days.

Surgery is an option, but is difficult and has many potential complications.  The pills are more commonly used.  They have some side effects of vomiting, diarrhea, and as with any pills, can be difficult to administer to a cat.

There is now a fourth option that has recently become available: nutritional management with Science Diet Y/D.  The idea behind this nutritional management is to deprive the body of iodine so that the thyroid gland does not have the building blocks to produce excess amounts of thyroid hormone.  The cat has to be on this diet exclusively (no other treats, no mice, no other cat foods) in order for it to be effective.

But there is controversy on the long term effects of iodine deprivation and the proteins in this diet are mostly derived from plant sources. Cats are obligate carnivores (meaning they have to have meat), and often plant proteins are not as readily available to them.

So there are several ways to manage or treat hyperthyroidism in cats.  There are pros and cons to all of them, and each must be discussed with your veterinarian to determine what means of control works best for the patient and “parent.”