Download Hyperthyroidism: Too Frisky!

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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.