Complete Care for Your Aging Cat - Amy Shojai [105]
Dr. Hager considers feline hyperthyroidism highly treatable. “It’s one of my favorite parts of the practice because first of all, I’m a cat person. Second, there are few things where the kitty comes in with something that’s relatively bad, and we send them home with a really high probability of curing them. We’re about to treat a 22-year-old kitty. That’s very satisfying.”
Senior Symptoms
Behavior changes are the most common symptoms of hyperthyroidism. Cats with concurrent diseases such as heart or kidney problems may have overlapping signs:
Increased appetite
Weight loss
Increased drinking and urination
Hyperactivity, pacing, short temper
Howling or yowling
Oily coat, hair loss, and/or rapid claw growth
Diarrhea or vomiting
Seeks cool place to rest
Diagnosis
Most commercial laboratories measure thyroid levels as a routine part of blood test in cats, says Richard Nelson, DVM, an internist at University of California-Davis. “That allows you to identify when those numbers start to go up.” However, the thyroid level can be artificially suppressed by other health conditions, says Dr. Hager. “That’s where the scintigraphy confirms and defines the problem.”
Also called a thyroid scan, scintigraphy employs a radioactive particle that seeks out and attaches to thyroid tissue, which is then revealed on a gamma camera. “It tells you if all the thyroid tissue is only in the neck right at the thyroid site, or other places,” says Dr. McCullough. Scintigraphy defines the extent of the disease, and helps the veterinarian choose the best treatment options. For instance, if the scan shows the thyroid tissue is limited to the glands in the neck, surgery to remove affected tissue may be a good option.
Dr. Hager says scintigraphy is currently the best method to confirm a diagnosis of hyperthyroid disease, figure out how much of the thyroid gland is involved, where the thyroid is located, and also whether the enlargement is due to a cancer or a benign adenoma (tumor). A tiny dose of a mildly radioactive but inert metal called technesium is injected into the cat’s vein, travels throughout the body, and within about 20 minutes it is preferentially taken up by thyroid tissue, salivary tissue, and the gastric mucosa.
“Technesium is the most commonly used imaging agent for nuclear medicine,” says Dr. Hager. “It has a very short half-life so it’s very safe, and it has a nice imageable photon that emits so we can pick up on the gamma camera.” After 20 minutes, the cat is gently placed on the flat-faced camera, and the inch-thick crystal inside the camera picks up the X-rays emitted from the cat’s body and glows in response. “That information goes to a computer that forms an image that tells us where most of the counts come from,” says Dr. Hager. “It gives us the anatomic definition. With cancer the radioactivity is scattered all up and down the neck, versus a localized benign process that’s sharp and well defined and in one spot in the neck.”
Hyperthyroid disease in cats can be treated three ways. “One is medical, two is to cut it out surgically, and three is do the iodine-131 [I-131 or radioactive] therapy,” says Dr. McCullough.
Surgery
When a benign adenoma is localized to the neck, surgery can be a permanent fix. But because most cats develop hyperthyroidism during their senior years, the risk of anesthesia and other health considerations are a concern.
“There are two thyroid glands, so sometimes it’s a big issue, do you take out just the abnormal one?” says Dr. Schulman. Over time, she says the normal lobe that is left behind in the surgery often also becomes abnormal, and begins causing symptoms all over again. The surgery can also be tricky. “The parathyroid gland sit right next to the thyroid, so if you take out both thyroid glands you run the risk of taking out all the parathyroid glands as well. Then you have a whole different