How to Spot and Treat Feline Hyperthyroidism

Diagnostic Dilemmas

Several common diseases of older cats share some clinical signs with hyperthyroidism. These include diabetes mellitus, chronic kidney failure, inflammatory bowel disease or intestinal cancer. It is not uncommon to diagnose an older cat with more than one of these conditions simultaneously. Your veterinarian will need to perform an array of diagnostic tests to reach the diagnosis of feline hyperthyroidism.

If your veterinarian suspects hyperthyroidism in your cat, the initial diagnostic tests generally include a complete blood count (CBC), blood chemistry panel, thyroid hormone analysis and a urinalysis. For most cats, these tests can confirm a diagnosis. However, up to 10 percent of hyperthyroid cats may have normal thyroid hormone levels in their blood, and the diagnosis in these cats may require some additional specialized testing.

What Do You Do If Your Cat Is Hyperthyroid?

Several treatment options are available. Each one has advantages and disadvantages, and your veterinarian will discuss the best plan for your cat. Here’s a brief overview of what they are:

  • Medication. Antithyroid medicine, called methimazole, is very commonly used and is highly effective at controlling hyperthyroidism. The medication can be administered orally or applied topically, which makes it more “user friendly” for some pet owners. Lifelong daily medication is required by most cats in order to adequately control their hyperthyroidism. Routine monitoring of bloodwork must also be performed in order for methimazole to be used safely and help minimize potential side effects.
  • Surgery. Surgical removal of the thyroid glands results in a cure of affected cats (except in those rare cases where the cancer has spread). Not all hyperthyroid cats are candidates for surgery though, usually because of concerns about anesthesia. Your veterinarian will determine if surgery could be an option for your cat.
  • Radioiodine treatment. Radioactive iodine therapy results in a cure of feline hyperthyroidism. An injection of radioactive iodine is administered and becomes concentrated in the abnormal thyroid gland(s), where it destroys the abnormal tissue. The procedure is not available at all veterinary hospitals — it must be done in a licensed facility and often necessitates a lengthy hospital stay. It can also be expensive for some owners.
  • Diet. There is one prescription diet available, which can be used to control hyperthyroidism in some cats. The thyroid glands require iodine from food in order to make thyroid hormones. This prescription diet contains very low iodine levels, so the diseased thyroid glands do not have the necessary ingredient to overproduce thyroid hormones. Strict adherence to this diet is imperative.

The prognosis for most cats affected by hyperthyroidism is good depending on how early it is detected and how well the cat responds to treatment or management options.
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