Recognizing And Treating Feline Hyperthyroid Disease

Older cats face unique health challenges. Some of these challenges are harder to detect than others. One example is feline hyperthyroid disease. Ten percent of cats over the age of 10 will develop hyperthyroid disease caused by tumors of the thyroid gland. These overactive thyroids cause cells in the body to consume more energy and oxygen and produce more than twice the normal amount of metabolic waste! This places a strain on the cat’s liver and kidneys. The heart rate in a hyperthyroid cat can be as much as 300 beats per minute compared to 120 beats per minute for a healthy cat.

hyperthyroid-catCats in the early stages of hyperthyroid disease can seem healthy. The older cat becomes very active, more vocal and has increased activity. Overweight cats transition to a more healthy weight. But, as the disease progresses, vomiting and diarrhea can develop. These cats don’t rest as well, they become irritable and don’t groom. Then they begin to lose weight at an alarming rate.

Fortunately, all of these symptoms can be reversed with treatment. Hyperthyroid disease can usually be controlled with medications, diet, surgery or with radioactive iodine treatment.

Medication (methimazole) can be given to control the levels of hormone produced by the tumor in the thyroid. The medication interrupts the production of the hormone, but does not resolve the tumor and must be given twice a day for the life of the cat. Common side effects are vomiting and diarrhea. This drug can also affect the liver and bone marrow. Skin reactions can occur as well.

Diet control involves a prescription food that is limited in iodine. Without sufficient quantities of iodine, the tumor doesn’t have the building blocks needed to produce the hormone that causes the symptoms of feline hyperthyroidism. Many foods contain some level of iodine, so no treats or food from the table are allowed. If there are other cats in the house, they all must eat the same special diet.

In the early phase of the disease, about 1 in 50 cats has a malignant tumor, but that rate increases to 1 in 5 in later stages. The size of a thyroid tumor increases considerably as time goes by, and more than one tumor usually develops, even when the disease is managed with medications and diet.

Surgery can be performed to remove the tumor, but due to the abnormal heart rate and function of cats with hyperthyroid disease, the anesthetic risks are higher. Seventy percent of cats develop tumors of both thyroid glands, making it necessary to perform two surgeries.

The most effective and safest treatment, which also has no side effects, is using radioactive iodine to kill the tumor. The thyroid tumor can’t distinguish regular iodine from radioactive iodine. When small amounts of the isotope are given, they damage the thyroid tumor cells and don’t affect any other cells in the body. There are no side effects with this therapy, but it does require a two-night stay in the hospital and contact is limited to 10 minutes per day for two weeks once they return home. The cure rate for early thyroid disease is 98% with a single dose.

If your cat is over eight years old and develops symptoms of thyroid disease, it is important to check with your veterinarian and discuss which option is best for your cat.

Originally published June 2015 In The Lake Norman Citizen

Dr. Tom Hemstreet is a veterinarian with LakeCross Veterinary in Huntersville where he also offers radioactive iodine treatment for cats with hyperthyroidism. The vets in the big yellow house have been treating pets like family for 20 years. For more information,
call 704-948-6300.