Download Feline hyperthyroid disease

The Scaredy Cat Hospital
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Feline Hyperthyroidism
A serious disease called “feline hyperthyroidism” has risen to epidemic proportions since the first cases were diagnosed in 1979. It is a
worldwide phenomenon, though worse in the U.S. than other countries. Hyperthyroidism (hyper = too much, thyroid = a hormonemaking gland), is seen mostly in older cats age 10 or more.
Thyroid hormone regulates the body’s basic metabolic rate. Too much of it is like drinking too much coffee—it speeds up every
reaction in the body.
Symptoms
Hyperthyroidism is typically the result of a benign thyroid tumor. Because the tumor cells are relatively normal, they continue to
produce thyroid hormones, resulting in a high level in the blood.
The most common symptoms of hyperthyroidism are:
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Increased appetite
Weight loss (often despite eating more)
Increased heart rate
Anxiety or “hyper” behavior
Howling at night
Increased thirst and urination
Vomiting
Diarrhea.
Not all cats will have all symptoms, and about 20% of hyperthyroid cats will be sluggish and depressed instead of hyperactive.
Untreated, hyperthyroidism can cause a serious heart problem called hypertrophic cardiomyopathy (thickened, enlarged heart) that
can ultimately be fatal.
Diagnosis In some cats, your veterinarian may be able to palpate an enlarged thyroid gland. However, hyperthyroidism is definitively
diagnosed by blood tests. An elevation in the total T4 or Free T4 by equilibrium dialysis (The Free T 4 test identifies the borderline
cases) is diagnostic. It is also common to also see elevated liver enzymes in hyperthyroid cats, so this may also help with the
diagnosis.
Causes. Many theories have been proposed to explain the dramatic rise in feline thyroid disease. Because it affects so many cats, the
focus has been on widespread, environmental causes.
Treatments. There are four primary treatment options for hyperthyroidism:
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Methimazole (Tapezole is the trade name) is a medication that can be given in tablet or liquid form (the tiny tablet can be
crushed and mixed into wet food) or as a topical gel (transdermal gel) that you rub on the inside of the cat’s ears (ideal for
non-pillable cats). It requires frequent blood tests for the first few weeks as the dosage is adjusted to fit the cat, and then
every six months to make sure the dose remains appropriate.
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Thyroidectomy is the surgical removal of the thyroid glands. A cat that has had both thyroids removed can still become
hyperthyroid again. These secondary tumors may form inside the chest, where they are inoperable. We do not recommend
this option.
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Radioactive Iodine is the most definitive treatment (cure). The thyroid uses iodine to make its hormones, and accumulates
large amounts of iodine. A single injection of radioactive iodine will be hoarded by thyroid cells and kill them, theoretically
curing the disease permanently. Most cats tolerate this procedure well, and most do not need thyroid supplementation. The
downside? The up-front cost is very expensive, and regulations require that the cat be kept in the hospital for several days.
However, dealing decisively with the problem may save money in the long run because no further treatment is needed in
most cats.
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Therapeutic diet is a relatively new option, with Hill’s Prescription Diet y/d canned and dry. We rarely recommend this
option.
Complications
Since hyperthyroid cats are typically older, many also have underlying kidney disease that may or not be obvious. The increased blood
flow caused by hyperthyroidism can actually help the kidneys and keep them functioning at a fairly normal rate. Lowering the thyroid
levels (by any treatment) lowers blood pressure and blood flow. This can “unmask” kidney disease that was always there but not
detectable.