The thyroid glands secrete
hormones (thyroxin [T3] and tri-iodothyronine [T4]), which regulate
the body's rate of metabolism. However, the system can go awry,
with increased (hyperthyroidism) or decreased (hypothyroidism) hormone
Within the last fifteen years, hyperthyroidism has emerged as a
new disease in cats 10 years and older. In fact, it now ranks as
one of the most common endocrine disorders in the cat, afflicting
one of every 300 cats seen at the Animal Medical Center in New York
It is not yet known whether feline hyperthyroidism is the result
of a primary thyroid disorder, or whether some factor(s) may be
stimulating the thyroid stands to produce an excessive amount of
Symptoms and Diagnosis
Typical symptoms of hyperthyroidism include weight loss, increased
appetite, hyperactivity, restlessness, increased fluid intake and
urination, vomiting, diarrhea, and muscle weakness. Often the coat
looks unkempt and dull. The heartbeat feels strong and rapid, sometimes
with noticeable arrhythmia. If you own a middle-aged or older cat
displaying these symptoms, you should schedule an appointment with
your veterinarian. The only sign we see consistently in all hyperthyroid
cats is weight loss. The other symptoms tend to appear later as
the disease progresses.
Because the symptoms can be suggestive of other diseases, your
veterinarian will probably suggest a complete blood count, routine
serum biochemical tests, and serum thyroid hormone concentrations
to aid in a definitive' diagnosis.
During the Physical examination the veterinarian will also feel
the neck region to determine if the thyroid glands are enlarged,
indicating hyperthyroidism. Either one or both glands may be affected.
In approximately 50% of cats diagnosed as being hyperthyroid, both
thyroid glands are diseased.
There are three basic forms of treatment available -- surgery,
anti-thyroid drugs, or radioactive iodine therapy. Each form of
treatment has its advantages and disadvantages. Your veterinarian's
choice of treatment will be based on several factors, including
the cat's age, and the presence of associated heart disease or other
If your cat has a one-sided thyroid enlargement, surgery may be
a good solution. Especially if he is hard to pill, if you’re
away a lot, or if he requires increasing doses of the anti-thyriod
pills (Tapazole). We have done this surgery on approximately 900
cats in the last 15 years. Most cats were over 12 and many were
12 – 16 years old. Survival rate has been 99.6%. The surgery
is not very traumatic for the cat because it is basically a minor
surgery done via a 1” long incision behind the “Adam’s
Apple”. The cost all inclusive is approximately $600-800.
If both thyroid glands are affected and the medication is problematic,
as discussed above then the radioactive Iodine treatment might be
a good solution.
Cats are treated with methimazole (Tapazole) which depresses the
thyroids output. Normally this pill is given twice per day and about
half of our patients will eat it ground in a favorite food. Adverse
reactions can occur but are very rare. Most common of these are
gastrointestinal signs – inappetance, vomiting and/or diarrhea.
These G.I. signs are dose size dependent and often appear when the
dose of Tapazole needs to be raised to 1 ¼ tab or 1 ½
tabs twice per day. We need to recheck thyroid levels initially
at 2 weeks and if regulated then every 2-3 months. This is done
via a simple painless blood tests.
Radioactive Iodine Treatment
This treatment modality is expensive, but is sometimes appropriate
especially if the patient is difficult to medicate, has both thyroids
enlarged, and/or has already had one thyroid removed wherein the
surgeon was unable to spare the BB sized parathyroid gland. Radiocat
in White Plains can handle this radioactive iodine treatment and
have your cat home in 3-7 days. Their number is 888 356-4131.