Your thyroid glands are responsible for your metabolism – temperature, weight maintenance, and many other systems in your body. They are two paired structures located in your neck alongside your trachea, and they function to secrete hormones, which are chemical messengers that help regulate the functions of your body.

Like you and other mammals, cats and dogs also have thyroid glands and, like you, there can be severe medical consequences when they don’t function properly.

In both dogs and cats, thyroid disease is the most common endocrine condition we treat. In humans, endocrinologists are doctors who specialize in diseases of the endocrine glands (thyroid, pancreas, adrenal, etc.). In veterinary medicine, your family veterinarian, with the help from veterinary internal medicine specialists, when needed, are your pet’s endocrinologists.

In cats, the most common thyroid problem we deal with is hyperthyroidism. This is when the thyroid gland produces too much thyroid hormone. Less than two percent of the cases of hyperthyroidism in cats are caused by a cancer of the thyroid gland.

Instead, the most common cause is overactive nodules within the thyroid glands that secrete too much hormone. The exact reason why this occurs in cats is not known, although environmental, nutritional and other factors have been researched over the years.

In general terms, too much thyroid hormone increases your cat’s metabolic rate. This can lead to muscle wasting, increased heart rate, changes in heart rhythm, and severe weight loss despite increased appetite. It can also cause increased drinking of water and increased urination, vomiting, diarrhea, weakness, and behavioral changes.

The primary method to help diagnose thyroid disease is a blood test to measure the total level of thyroid hormone. This is one of the reasons why annual exams and lab screening are so important in middle age and older cats.

There are three traditional means of managing feline hyperthyroidism. Surgical removal of the affected gland or glands is one option, although there are possible complications with this method that can be significant.

Treatment with radioactive iodine is a common treatment option for both people and cats. This is a noninvasive technique that targets the hyperactive thyroid tissue, but spares the normal cells. The disadvantage of this option is the cost, which can range from $875 to $1500.

The third method for managing hyperthyroidism is the daily administration of methimazole. This medication blocks the effect of the thyroid hormone, although it does not keep the affected nodules from continuing to enlarge. Adverse reactions to methimazole, sometimes severe, occur in about 10 percent of cases, and some cats become resistant to the medication.

Veterinarians now have a nutritional option that may also be considered to help manage this condition. After 10 years of researching the relationship between dietary levels of iodine and feline hyperthyroidism, Hill’s Pet Nutrition has released a new prescription diet called y/d. The theory is that limiting the dietary iodine in hyperthyroid cats will result in the normalization of thyroid levels over time.

With this new tool, veterinarians can start treatment with food alone and then use medications or radioactive iodine if the diet is not an option for an individual cat or if the diet alone failed to control the disease.

Thyroid disease is one the major problems we see in middle aged cats. Please consider routine annual visits with lab screening for your cats to help keep them healthy. For additional information about y/d, visit the Hill’s Pet Nutrition website at  www.hillspet.com/products/pd-feline-yd-dry.html.

Dr. Kiel is the U.S. Army veterinarian currently supporting NAS Whidbey Island and Naval Station Everett. His columns appear the first and third Friday of each month. Please send questions or comments to Dr. Kiel at joseph.kiel@navy.mil.