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What is hyperthyroidism?
Hyperthyroidism
is the condition resulting from
secretion of excess thyroid hormone. In cats, this usually
results from adenomatous hyperplasia or adenoma (benign tumor) of the
thyroid gland. Carcinoma (cancer) is a very rare cause of
hyperthyroidism in cats.
How can hyperthyroidism be treated?
Hyperthyroidism
can be treated medically, surgically,
or with radio iodine. Medical treatment consists of
administration
of methimazole (Tapazole) one to three times per day. Methimazole
treatment will usually control hyperthyroidism but is not a cure (i.e.,
the drug will block thyroid hormone secretion but will not remove the
thyroid tumor), and the drug must be given for the rest of the cat's
life. Surgery will cure the hyperthyroid condition and consists
of the removal of part or all of the thyroid gland (the feline thyroid
gland consists of two separate lobes). Radio iodine (radioactive
iodine) will also cure the hyperthyroid condition. The procedure
for this treatment is relatively simple, consisting of a single oral
dose.
Why would radio iodine be used instead of medicine or
surgery?
Medical
therapy will work for some cats, but there can
be several reasons it may not be the best choice. First, some
cats are difficult or impossible to pill. Second, mild reactions
(e.g. loss of appetite, vomiting) are common, whereas a few cats
develop serious adverse reactions to the medication (blood or liver
problems). Because of these side effects, periodic blood tests to
monitor the cat's condition are necessary. Finally, some owners
may not want to have to medicate their relatively young cat for the
rest of its life (pills must be given daily).
Surgery
is generally an effective treatment for
hyperthyroidism but may have disadvantages in some cats. Many
cats with hyperthyroidism have heart problems and are higher anesthetic
risks. There is also a risk that there will be temporary damage
to the adjacent parathyroid glands during thyroid surgery resulting in
hypocalcemia (low blood calcium). This complication can be life
threatening and result in extra hospitalization and cost. After
surgery, some cats will develop hypothyroidism and will require
treatment with thyroid hormone pills for a period of time.
Finally, there is a small risk that the hyperthyroidism will not be
cured with surgery or the condition will reoccur.
Radio
iodine therapy has some distinct advantages over
use of medical or surgical treatment. With radio iodine, the need
for anesthesia and the risk of hypocalcemia (the major disadvantages
with surgery) are eliminated. Tapazole treatment is not needed; in
fact, drug treatment must be discontinued for at least two weeks before
radioactive iodine is given. The major draw back is that after
administration of radio iodine, the cat must be kept hospitalized for a
period of 4 (four) days.
How does radio iodine therapy work?
Iodine
is an element required for normal health.
In the body, it is used primarily by the thyroid gland (located in the
neck) to produce the thyroid hormones (T4 and T3 are the two major
thyroid hormones).
Radio
iodine hyperthyroidism is a form of iodine
that has been made radioactive. In it's radioactive state, it
undergoes a natural process (decay) in which it gives off
radiation. The radiation given off consists of three types:
alpha, beta and gamma. The half-life of I-131 is eight days; in
other words, one-half of the radio iodine goes through this process
every eight days.
When
taken into the body, a large percentage of
radio iodine accumulates in the thyroid gland. The remainder of
the I-131 is excreted in the urine and feces. Once the radio
iodine is taken up by the thyroid gland (or thyroid tumor in a
hyperthyroid cat), the gamma rays and beta particles are
released. The beta particles are particularly lethal to the
thyroid tumor cells. The beta particles travel a maximum of 2-5
mm in
tissue; therefore, beta-particles are locally destructive but spare
adjacent hypoplastic thyroid tissue, parathyroid glands, and other
cervical structures. The radiation destroys the thyroid tumor
cells and thus treats the hyperthyroid condition.
How is the therapy given?
The
radio iodine is given as a single dose on the first
hospital day. After the treatment is administered, your cat is
placed in isolation. In this case, isolation means keeping your
cat in a separate "facility", away from other animals not receiving
this treatment. Your cat is then monitored over the next four
days until the cat's radioactivity level is low enough to permit his or
her return to you.
How long is the hospitalization period?
The
half-life of the iodine used is eight days.
The iodine is excreted primarily in the cat's urine. The usual
period is four days.
How do I check on my cat's condition during
treatment? Is visiting allowed?
Due
to the nature of the treatment, visitation is not
permitted. The cats are fed and monitored two to three times
daily by a full-time veterinary technician and Dr. Marshall during
their stay. If you wish, you can call us to check on the status
of your cat.
Are there any side effects or risks of therapy?
Since
the iodine is specific in its site of action,
there is no hair loss or increase in skin pigmentation, as may be seen
with other forms of radiation therapy (cobalt radiation). Some
cats seem to experience mild discomfort of the thyroid region
(thyroiditis) at the beginning of therapy, but this resolves itself
spontaneously and does not cause a problem.
Occasionally
a cat will develop hypothyroidism
(under-active thyroid gland) after treatment with radio iodine.
This is easily controlled with supplementation and may not be
permanent. Overall, side effects are extremely rare.
What happens after the isolation is over?
You
will need to wear latex gloves when scooping the litterbox. Much
of the residual radioactivity will be eliminated through your cat's
urine and feces. Therefore, we recommend that your cat be
provided with a litter box that has a liner and utilizes flushable
style cat litter. After changing the litter, your hands should be
washed thoroughly.
Upon
discharge, your cat will still be minimally radioactive. Even though
the level of radioactivity is very low (much lower than the level at
which human patients are discharged from the hospital) you should still
exercise caution during this period.
All
of the remaining radioactivity in your cat will gradually disappear
over the next 2-4 weeks (through radioactive decay and excretion into
the urine). Until this is complete, your cat will emit low levels of
radiation. Because of this, we require that you also isolate your cat
at home for one week further, two weeks if children are living in the
household. This isolation can be any spare room in your home.
What aftercare will my cat need?
The
vast majority of cats require no specific aftercare. Your
veterinarian should perform a complete blood
analysis after the two week isolation, then monitor the thyroid
function three months after, and then on a six month basis as a part of
their on-going health care plan for your pet.
Does the radio iodine treatment always work to cure
the hyperthyroidism?
Our
studies have shown that a single dose of
radio iodine is effective in curing hyperthyroidism in over 97% of cats
that are treated. Even those cats that are not completely cured
after one treatment, however, show some lowering in their circulation
thyroid hormone concentrations and improve clinically.
If
hyperthyroidism persists for longer than three to
six months after treatment, re-treatment with radio iodine is generally
recommended to cure the disorder. Virtually all cats that remain
hyperthyroid after the first treatment are cured by the second
treatment.
Can the hyperthyroidism ever reoccur?
Yes,
although it is very uncommon (less than 3% of cats
treated). In addition, such reoccurrences usually develop three
years or longer after the hyperthyroidism was first
treated. Therefore, such relapses may indicate the
development of a new thyroid tumor causing hyperthyroidism, rather than
relapse from the first tumor that was treated with radio iodine.
What do I do on the day of treatment?
Please
bring your cat to the hospital at the scheduled
time. You should feed your cat on the day of admission to the
hospital (fasting is not necessary). Your veterinarian should
have done all or the majority of tests necessary before treatment; if
further tests are required, they can be performed by us but treatment
may then have to be postponed. If your cat has been on
methimazole (Tapazole), this drug must be discontinued for at least two
weeks prior to treatment.
Should I bring anything for my cat?
If
your cat eats a particular kind of food, we suggest
that you bring a few cans so that we know exactly what you want your
cat to eat during the time of hospitalization. Also, you will need to
leave a carrier with us for the ride home as your cat is required to
ride in one while on the way home. We will also need you to bring your
cats x-rays. Personal items (a
sock or toy) to place in your cat's cage are not allowed due to
contamination.
What happens on the day of admission?
A
full explanation of hyperthyroidism treatment
will be gone over with you. If all of the other routine blood
tests have been done by your veterinarian, we will treat your cat on
the day of admission.
Is radio iodine therapy expensive?
The
cost of any treatment for feline hyperthyroidism is
significant. The cost for radio iodine therapy is generally a
total fee of
$1,100.00, but may be more if the hyperthyroidism is severe. This
includes the radio iodine itself, the cost of hospitalization, food,
litter, and monitoring. Tests required prior to therapy are not
included. This compares reasonably with most fees for surgical
removal. The cost of medication would average $400 to $500 per
year plus the cost of repeat blood tests.
Please
note, because we must order the dose of
radio iodine before the treatment is administered, cancellation of a
scheduled appointment (less than 48 hours before the appointment time)
will result in a charge of
$250.
How do I pay for radio iodine therapy?
Payment
is required at the time of service. As
far as method of payment is concerned - cash, checks or charge cards
(Visa, MasterCard, or Discover) are accepted.
Five
Locations for Cats Radio iodine Treatment Centers
- Greater
Detroit Area:
Dr. Dan Marshall (Director)
Cats Veterinary
43727 Gratiot
Clinton Township, MI 49036
(586) 463-9550
- Southern
Michigan and Northern Ohio:
Dr. Jeff Dizik, Lincoln Park Veterinary
Hospital
3909 Fort Street
Lincoln Park, Michigan 48246
(313) 389-2222
- Northern
and North-Western Suburbs:
Dr. Steven Bailey
Exclusively Cats
6650 Highland
Waterford, MI 48328
(248) 666-5287
- Western
Michigan:
Dr. Tammy Sadek
Kentwood Cat Clinic
3215 Breton Rd. SE
Kentwood, MI 49512
(616) 241-6369
- Lansing
Area:
Dr. Kristine Stalling
House
Calls Veterinary Clinic
14080 Wright Rd
Eagle, MI 48822
(517) 626-6900
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