Feline Hyperthyroidism In Aging Cats

Original Article by Dr. Jack Stephens for Pets blog

Hyperthyroidism is a pet health issue that occurs in cats over the age of eight. The majority of cats that develop the disease are 10 years old or older. Hyperthyroidism is caused by an overactive thyroid gland. The excessive thyroid hormone overstimulates the body causing a cat to become overactive and have an increased appetite. In this article, we’ll lay out the symptoms, available treatments, and prognosis for cats with hyperthyroidism.

Feline Hyperthyroidism Symptoms

The number one symptom of feline hyperthyroidism is rapid weight loss. Hyperthyroidism causes cats to lose weight even though they have a ravenous appetite. Other symptoms of feline hyperthyroidism can include increased thirst, vomiting, diarrhea, and an unkempt coat. Cats with hyperthyroidism will also have an increased heart rate. This increase in heart rate can cause damage to the heart and if left untreated can lead to heart failure and eventually death. Eye problems are also a potential symptom that can develop in untreated cats with hyperthyroidism.

Feline Hyperthyroidism Treatment

Your veterinarian will run blood tests to evaluate the levels of thyroid hormones in your cat’s blood if hyperthyroidism is suspected. Blood tests will also be run to rule out other diseases with similar symptoms. Both diabetes and kidney failure can cause weight loss in cats⁶. The blood work will let the veterinarian know how well the other organs in the body are functioning. Once a diagnosis of hyperthyroidism has been made, a cat can begin treatment and get relief from its symptoms.

In many cases, hyperthyroidism in cats is treated with an oral medication containing methimazole. Sold under the brand names Tapazole and Felimazole, methimazole is the only active ingredient currently approved by the FDA to treat the disease³. The goal with these drugs isn’t to cure the disease, but to control it and help the animal feel better. There is no reason why a cat afflicted with hyperthyroidism can’t live a normal life well into their senior years with this course of action. Daily administration of the medication, however, is necessary for the remainder of a cat’s life and periodic visits to a veterinarian are needed to monitor the animal’s health. As with any medication, treating hyperthyroidism with a drug can cause side-effects. The side-effects of methimazole include depression, vomiting, and lack of appetite.

Treating Feline Hyperthyroidism with Diet

A prescription diet that limits the amount of iodine is another option for treating hyperthyroidism⁴. There are, however, some concerns regarding the long-term effects of iodine restriction on a cat’s overall health. Talk to your veterinarian to see if this option is viable for your cat. 

Other treatments for hyperthyroidism include Radioactive Iodine Therapy and surgery. The goal of the first of these options is to destroy the abnormal thyroid tissue without harming other organs. The therapy is given as an injection and thus does not require anesthesia. Surgery is a less common treatment that requires anesthesia and can cause risk to an older cat's heart or kidney. The invasive nature of surgery can make many cat owners leery of this treatment option for hyperthyroidism. With both of these options, the cost can be a factor and therefore not viable for a number of pet parents.

Prognosis for Feline Hyperthyroidism

As with any disease, early detection and proper treatment based on the cat’s general health and age will lead to the best outcome. A very small number of cats with hyperthyroidism have cancerous growth of the thyroid gland, so the prognosis for cats with the disease is good. Unfortunately, there are no known preventive measures cat owners can take to avoid hyperthyroidism.