Radioiodine Therapy
What is hyperthyroidism?
The thyroid glands sit on either side of the voicebox. They produce
hormones that control the body's metabolism (e.g., how fast food
calories are
burned, how much inhaled oxygen is used, and how rapidly the heart
beats). In other words, how fast your cat's "engine is revving" depends
on how much thyroid hormone is produced. Older cats often develop a
benign growth in one or both thyroid glands, resulting in excessive
hormone production.
What are the signs of hyperthyroidism?
Hyperthyroid cats tend to lose weight despite a ravenous appetite.
They may drink excessive amounts of water, have diarrhea, vomit intermittently,
and become hyperactive or irritable. The heart rate is elevated and
sometimes irregular. Your veterinarian may be able to hear a heart
murmur and feel an abnormal nodule in the thyroid region.
 Is there a test for hyperthyroidism?
Your veterinarian can do a blood test to measure
the thyroid hormone level. Confirming hyperthyroidism is very important
because other problems such as diabetes, heart disease and inflammatory
bowel disease can mimic the signs of hyperthyroidism. Older cats may
have multiple health problems, so a complete physical examination, bloodwork
and urine screening are always indicated.
Survival Time Double with I-131 Therapy*
*JAVMA, Vol. 228, No 4, February 15, 2006
How does radioiodine therapy work?
A radioactive isotope of iodine is injected and
travels through the bloodstream. It is taken up selectively by the thyroid
glands because they require iodine to manufacture thyroid hormone. Other
tissues do not use iodine. The radioactive iodine releases tiny atomic
particles called beta particles. Because the beta particles travel only
short distances and are in much greater concentration in active thyroid
tissue, radiation damage is restricted to the abnormal thyroid glands.
If only one gland is hyperactive, the other gland shuts down hormone
production so a normal gland does not absorb iodine and is not affected.
Therefore radioiodine is like a painless magic bullet that affects only
the abnormal thyroid tissue.
What is the treatment procedure?
A recent physical examination, bloodwork and urine
testing are required to rule out concomitant diseases. If a heart problem
is suspected, chest x-rays and an echocardiogram are recommended. Any
unrelated issues should be stabilized prior to admission; if necessary
a consultation with a veterinary internist can be arranged. After the
radioiodine injection, your cat is boarded in a shielded medical ward
until the radioactivity level fades (four days). All cats have their
own oversized cage facing a large window to the outside so they can indulge
in one of their favorite activities. They are given fresh food and water
twice daily. You are welcome to provide favorite foods as well as any
medication or nutritional supplements. You are updated every other day
on your cat's condition by telephone or the Internet. You can call with
questions at any time during business hours.
Will my cat be radioactive?
Yes, but only temporarily because the iodine is
eliminated in the urine and feces. Because bedding and toys could become
contaminated during hospitalization, they cannot be returned to you if
you provide them. Once your cat is released, some limitations to your
interactions and special handling of the litter are recommended. Detailed
instructions, bags and gloves are provided when your cat returns to your
home.
Can I visit my cat during hospitalization?
State regulations do not permit visitors in the
radioiodine therapy room. We have continuous video
monitoring of the
therapy room and you can "visit" your cat anytime via the Internet.
Cats may not be removed prematurely form the ward for any reason.
Are there any complications?
Radioiodine therapy does not have any of the risks
associated with surgical or medical treatment. In about five percent
of cats, the hormone level may stay high and require re-treatment, which
is done at no extra cost during the first year. It is even more rare for the hormone levels
to become too low after radioiodine treatment. If this should occur,
your cat would require supplementation with oral thyroid hormone.
What follow-up is necessary?
Thyroid levels should be measured at 1, 3 and 12
months post-treatment by your regular veterinarian.
 The best and safest treatment
Radioiodine therapy is currently the best and safest
treatment available for feline hyperthyroidism. It cures the disease
painlessly and efficiently, and restores the health and quality of life
you and your cat are longing for.
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