Hyperthyroidism is the most common endocrine disorder for cats middle aged and older cats, but early progression of the disease might fly under the radar for many cat owners. 

If your cat is getting up there in years, it’s important to learn about hyperthyroidism so that you can make sure your cat can lead a long and happy life.

What is feline hyperthyroidism?

The thyroid is a gland located in the neck — cats have two lobes, one on each side of the windpipe. The thyroid is responsible for producing thyroid hormones that regulate metabolism and  key body processes.  

The vast majority of hyperthyroid cats have a benign tumor called an adenoma on one or both of their thyroid lobes. Less than 3 percent of feline hyperthyroid cases are caused by malignant, cancerous tumors (carcinoma). These tumors ramp up thyroid hormone production. 

Hyperthyroidism occurs when the body has too many thyroid hormones. These hormones are called thyroxine (T4) and triiodothyronine (T3).  

Too many thyroid hormones throw off your cat's body systems, causing several different problems. Signs of hyperthyroidism include: 

  •  Weight loss 

  • A huge appetite 

  • Increased thirst and urination  

  • Vomiting  

  • Diarrhea  

  • An unkempt coat  

  • Increased vocalizations 

  • Increased activity

Rarely, some hyperthyroid cats might become lethargic or eat less.  

“Other conditions that can present similary to hyperthyroidism include diabetes, disease of the small intestines (inflammatory bowel disease or lymphoma), and chronic kidney disease,” said Stefaine DeMonaco, clinical associate professor in internal medicine at the Virginia-Maryland College of Veterinary Medicine.  

Hyperthyroidism typically occurs in middle aged and older cats. It’s a common disorder. About 10 percent of cats 10 years of age or older develop hyperthyroidism.  If ileft untreated eventually the disease can become severe enough to lead to complications such as heart disease and, rarely, high blood pressure.  

“The best way to look out for hyperthyroidism is to watch for any symptoms of the disease such as weight loss with a good to increased appetite,” DeMonaco said. “Some owners might notice their older cats are acting young again by being more active.  Routine wellness exams in older cats can detect unexplained weight loss that might indicate hyperthyroidism as well as checking thyroid levels. “

Prevention and treatment

Researchers don't yet understand the causes behind feline thyroid tumors, though it's likely a combination of genetic and environmental causes. There is no known way to prevent feline hyperthyroidism. 

 Your veterinarian can check for an enlarged thyroid and run tests to determine if your cat has hyperthyroidism. There are multiple treatments available for hypothyroidism. These include:

  • Medications that help manage the disease  

  • Radioactive iodine treatment 

  • Dietary therapy 

  • Surgery to remove the thyroid

You and your veterinarian can work together to find the right treatment option for your cat’s unique needs.

“Once a cat is diagnosed with hyperthyroidism and started on treatment, monitoring includes measuring thyroid hormone levels to make sure they are not too high or too low,” DeMonaco said. “About 25 percent of hyperthyroid cats have kidney disease that cannot be detected until hyperthyroidism resolves.  Therefore, it is also important for kidney function to be monitored.”

If not treated, hyperthyroidism can progress, leading to more and more health complications for your cat. With veterinary care, however, your hyperthyroid cat can get healthier — most cats respond well to treatment and go on to live for many more years.

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