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“We Speak Cat” 1476 University Avenue Phone: 920-435-2287 Green Bay, WI 54302 Fax: 920-435-7898 www.mycatcareclinic.com Hyperthyroidism: Too Frisky! When Elaine Franklin’s 10-year-old calico cat, Samantha, started to race around the house every night, Franklin was somewhat pleased at the transformation of her usually lethargic feline companion. It was a bit of a nuisance, but Samantha seemed to be experiencing a second kittenhood, and Franklin thought it wasn’t a bad thing for the somewhat tubby cat to get exercise. At Samantha’s next visit to the veterinarian, Franklin was shocked to discover that her cat had a condition known as hyperthyroidism that was the cause of the increased activity. Hyperactive behavior: a common sign Hyperthyroidism occurs when the thyroid gland, located in the neck, begins to overproduce hormones (T3, or triiodothyronine, and T4, or thyroxine), which are important for metabolism. The reason for the hormone overproduction is most commonly goiter, a swelling of the thyroid gland, which is usually due to the presence of a benign thyroid tumor. Hyperthyroidism is extremely common in cats 8 years old and over. The behavioral manifestations are so typical that veterinarians will screen older cats who show marked behavioral changes for hyperthyroidism right away, according to veterinary internal medical specialist Thomas Schermerhorn, VMD, of the Department of Molecular Medicine at Cornell’s College of Veterinary Medicine. The veterinarian will take blood samples to measure T4 levels. The insidious aspect of the disease, Dr. Schermerhorn points out, is that most owners, like Franklin, assume the increased activity is merely a new lease on life. The often also don’t notice that their cat is losing lots of weight-another result of the disease-since they see their cat every day. Indeed, Samantha had developed a voracious appetite, yet she was losing weight, a factor that came to light when the veterinarian put her on a scale. Behavioral signs Because the behavioral signs are classic, it’s easy to be on the lookout. Hyperthyroidism affects the cat’s behavior in two ways. The disease causes physiological hunger to the extent that the cat may even jump on the table to eat the owner’s food or break into a cupboard. It also has a direct effect on nerve tissue—essentially, the overabundance of hormone is toxic to the nervous system. Typical behavioral changes include restlessness and, in some cats, aggression. Many hyperthyroid cats can’t tolerate being restrained, may pace, and exhibit what Dr. Schermerhorn calls “the hyperthyroid stare.” They have a strange focus, he says, “where they’re looking at you, but not quite seeing you.” In a few cases, the cat may become extremely listless. This may occur after the other more typical behavioral changes. The degree of thyrotoxicity may vary from cat to cat, so the behavioral effects may not be exactly the same. Complications The physiological effects of hyperthyroidism include hypertrophy—or enlargement—of the heart and hypertension. Essentially, thyrotoxicity causes the whole body to go into overdrive. To treat it, veterinarians may prescribe an antithyroid drug such as Tapazole (methimazole). Long-term use of such drugs is necessary for the rest of the cat’s life unless curative measures include thyroidectomy (surgical removal of the gland) and treatment with radioactive iodine, which destroys the hormonemanufacturing tissue of the gland. Hyperthyroidism and kidney failure An interesting side effect is that the hyperthyroidism compensated for kidney failure, another plague of elderly cats. When the hyperthyroidism is treated, the kidney failure becomes evident. With really elderly cats, the question, as Dr. Schermerhorn puts it, is “whether you want to exchange bad for worse” by treating the signs of hyperthyroidism, only to unmask the kidney disease. It’s like “walking a tightrope,” he says. It is possible, says Dr. Schermerhorn, to pharmacologically mimic the absence of a thyroid gland in an elderly cat to gauge, in advance, the effect treatment for hyperthyroidism will have with respect to underlying kidney disease. Watch for These Signs Any of these signs may indicate that your older cat (8+ years) may have hyperthyroidism. It’s important to have your veterinarian examine her and confirm the presence of the condition with a blood test. *Weight loss, often with extreme hunger *Irritability *Hyperactivity *Unkempt appearance *Increased urine volume *Vomiting *Diarrhea The Cures for Feline Hyperthyroidism If untreated, an overproductive thyroid gland can cause a cat to waste away and die. It’s always a pleasure to see your cat come running to you at mealtime and dig enthusiastically into its chow. Apparently you’re feeding it the right stuff. But there’s a limit. A cat that never stops looking around for food and that never fails to eat everything that’s put in front of it (and whatever else it can sink its sharp little teeth into) may be in serious trouble. Such an insatiable appetite—especially if accompanied by noticeable weight loss—is one sign of a glandular disease called hyperthyroidism. If the condition persists and remains untreated, a cat can eventually waste away and die, no matter how much food it eats. Small but Crucial Feline hyperthyroidism is a condition caused by a malfunctioning thyroid gland, a relatively small structure with two lobes, right and left, that are situated in a cat’s neck adjacent to the upper end of its trachea, or windpipe. It is a crucial component of an animal’s endocrine system, a varied set of glands located throughout the body that secrete hormones into the bloodstream and thereby regulate many vital bodily processes. The adrenal glands, for example, secrete hormones that help keep blood pressure and heart function in check and control the body’s use of fats, proteins and carbohydrates while the pancreas produces the hormone, insulin, that regulates blood sugar. The thyroid glands function, on the other hand, is to regulate an animal’s overall metabolism—the speed at which all of its bodily processes are carried out. The thyroid gland accomplishes this by secreting two vitally important hormones—commonly known as T3 and T4—that circulate through the system and stimulate receptors on the internal organs. When the thyroid is operating properly, an animal’s metabolic rate is smoothly maintained. When the gland secretes either too much or too little T3 and T4, all of a cat’s bodily processes either accelerate or slow down, and the animal can eventually end up in big trouble. Excessive Production Hyperthyroidism, a dysfunction of the thyroid gland that is frequently observed in older cats, is marked by excessive hormonal production. “The condition usually results from one or more tumors in the thyroid gland.” says Mark Peterson, DVM, head of the endocrinology division at the Animal Medical Center in New York City. “The tumors are almost always benign hyperplasias, growths that result from an overproduction of noncancerous cells. Only one percent or so of the growths associated with feline hyperthyroidism are cancerous.” For reasons that remain unknown, says Dr. Peterson, the presence of a benign tumor will precipitate excess hormone production and, as a consequence, an acceleration of most bodily processes. This speed up will gradually result in signs that may be noticed by the animal’s owner, such as persistent gain in appetite accompanied by an apparent loss of weight or a visible deterioration of a cat’s hair coat. Other consequences, however, will not be clear to the owner. One especially dangerous condition that can be precipitated by hyperthyroidism is thyroid induced cardiomyopathy, a potentially life threatening disease of the heart muscle. This condition will most likely be spotted during a routine physical examination when a veterinarian notices a suspiciously rapid heartbeat. The presence of cardiomyopathy is then confirmed by ultrasound examination. Is There a Typical Patient? The condition is the most common hormonal, or endocrine, disease observed in cats, says Dr. Peterson, noting that three or more cats are diagnosed with hyperthyroidism each week at his clinic. “About 90 percent to 95 percent of the patients are 10 years of age or older,” he says, “and the average age is about 13. The only reason that the average age isn’t higher is that when cats get to be 16 or 17, they die of other diseases. We’ve seen it in young cats, but in general you can consider feline hyperthyroidism to be an older-age disease.” There is no gender predisposition for the disease, he adds, and although Siamese cats are possibly at greater risk than other cats, no significant breed disposition for the condition has been convincingly identified. Clear Indicators Increased energy and hyperactivity are among the indications that a cat is suffering from hyperthyroidism. These indications may surface in connection with the animal’s increased appetite. “It’s not unusual,” says Dr. Peterson, “for a cat to wake up its owner in the middle of the night or early morning crying out for food. And as the disease progresses, the cat may become irritable and very nervous as well. It may lick itself excessively and develop bald spots, and it may neglect to use the litter box.” In addition, the cat is likely to vomit frequently after eating and to have frequent b outs of diarrhea, while at the same time experiencing progressive weight loss as the animal continues to increase its intake of food and water. The owner may not notice the weight loss when it amounts to only a half pound or pound. “But eventually,” Dr. Peterson says, “it will become obvious to the owner. If not, a veterinarian will probably spot the weight loss in the course of the cat’s yearly physical exam.” Confirming Suspicion Fortunately, says Dr. Peterson, hyperthyroidism is familiar to veterinarians and relatively easy to diagnose. He describes the diagnostic procedure, which he recommends for all cats over age eight who are losing weight while eating normally or excessively, as follows: “A suspicion of hyperthyroidism is based on the cat’s history, clinical signs and abnormalities that show up in a physical examination. In most cats, an enlarged thyroid nodule can be felt in the neck. “A tentative diagnosis of hyperthyroidism is confirmed by measuring a high level of the T4 hormone circulating in the blood. Just a single blood test will be 90 percent to 95 percent accurate in making a definitive diagnosis.” Treatment Methods The condition can be treated medically, surgically or with radioactive iodine. Medical treatment consists of the administration of methimazole (Tapazole) in a pill form three times per day. The medication usually controls the disease, but it is not a cure. It will block the secretion of thyroid hormones but will not remove or destroy the tumor responsible for the condition. Most owners decline medical treatment, says Dr. Peterson, since the pills, costing about a dollar per day, will have to be administered daily for the rest of the cat’s life, and the dosage may have to be increased periodically. Furthermore, the medicine may have undesirable side effects, such as vomiting. And, he adds, some cats are very difficult to “pill.” Surgical treatment, which remedies the hyperthyroid condition, involves removal of all or most of the gland. Sometimes only one of the two lobes is removed. According to Dr. Peterson, surgery was once the treatment of choice among veterinarians, but is much less frequently used today. “Not that it’s a bad treatment,” he says, “but there are problems associated with it. The thyroid itself is easy enough o remove, but there are small glands—the parathyroid glands—located near the thyroid and even partly within the gland itself. These tiny parathyroids regulate a cat’s calcium levels, and if they are damaged or removed by accident, which is pretty easy to do when you’re removing the entire thyroid, the animal will have another disease introduced that’s even worse than hyperthyroidism.” Radioactive iodine treatment, says Dr. Peterson, is currently the treatment of choice. The procedure is comparatively simple, consisting of a single dose of radioactive iodine that is usually administered by means of a single injection under the skin, although it may also be given orally or intravenously. “This method is effective,” he says, “because iodine is normally an ingredient of the thyroid hormone. When the iodine is made radioactive, it still gets taken up by the gland to make the hormone, but when it gets into the tumor it gives off radiation that destroys the growth.” Treatment with radioactive iodine is relatively expensive—typically ranging from $1,200 to $1,500. “But it’s a one-time treatment,” says Dr. Peterson, “that is 95 percent successful and will relieve a cat’s hyperthyroidism for the rest of its life.” Following any of the three treatments, he notes, a cat will regain its normal dietary and behavioral patterns “right away,” although it may take two or three months for its weight to return to normal. All information taken from CatWatch.