Radioiodine Treatment For Feline Hyperthyroidism
What is hyperthyroidism?
A condition resulting from excessive secretion of thyroid hormone.
This is the most common endocrine disorder in cats.
The thyroid gland becomes over active either from adenomatous
hyperplasia or adenoma of the thyroid gland. Very rarely it can
be from malignant carcinoma of the thyroid gland.
Clinical symptoms are variable and include:
Weight loss
Hyperactive
Increased appetite (or decreased appetite)
Drinking and urinating more volume
Rapid heart rate
How to diagnose feline hyperthyroidism:
A simple blood test to measure the T4 value.
Occasionally, more sophisticated test may be done when the Free
T4, T4 values are normal but hyperthyroidism is still suspected
(T3 suppression test or a TSH test).
What are the most accepted treatment options?
SURGERY – remove the abnormal thyroid gland. Risks include
increased anesthetic risk, damage to the parathyroid gland resulting
in abnormal blood calcium. The other thyroid may become overactive
in at least 30% of cats.
MEDICAL – daily administration of an antithyroid drug such
as tapazole. Some cats are difficult to pill. Mild to severe reactions
to the drug can occur including vomiting, anorexia, low platelet
count, low white blood cell count and liver disease.
RADIOIODINE – treatment of choice. Administration of a single
subcutaneous injection of radioiodine. Simple, effective and safe
with up to a 95% success rate. Duration of hospitalization is
usually 3 to 7 days and is determined solely by Geiger counter
readings of the patient.
How does it work?
The only place the body uses significant amounts of iodine is
in the thyroid gland (to make thyroid hormone). Therefore, when
the radioactive substance is tied to iodine, the combination ends
up in the thyroid gland. The radioactive substance is taken up
primarily in the overactive abnormal thyroid cells and destroys
them gradually, preserving adjacent healthy thyroid cells.
What happens to my cat during the hospital stay?
Bring all your cat’s favorite foods to eat while he/she is
here.
A Color Doppler Echocardiogram will be performed while your cat
is here to check for thyrotoxic heart disease or other heart problems
occurring in cats. This is a non invasive procedure.
Your cat will remain in the hospital for 3 to 7 days.
Every day, he/she will be monitored for radioactive levels using
a Geiger counter.
As soon as the levels are safe (as determined by state regulations)
he/she can go home.
After care for the first two weeks at home.
Hold your cat for up to 15 minutes per day then wash your hands
when done.
Keep in doors.
Use disposable latex gloves when changing the litter box. Use
flushable litter or seal litter in a plastic bag and place outside
in your trash container.
After two weeks, your cat will have lost essentially all of his/her
radioactivity and you and your cat may return to your cat’s
normal routine.
Follow up blood test.
Have your veterinarian check a BUN and T4 in one month, then a
T4 in three months, then a T4 once a year.
