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Radioiodine Treatment for Hyperthyroid Cats
Why is radioiodine the treatment of choice for hyperthyroidism?
The thyroid gland normally uses iodine absorbed from food in the production of
thyroid hormones. When a functional thyroid tumor develops, normal thyroid tissue
shrinks because thyroid hormone production by the tumor is excessive. When radioactive
iodine (131 I) is given, it is rapidly absorbed by the hyper functioning thyroid
tissue, even tissue in abnormal or surgically inaccessible locations. Because the
radioiodine emits beta and gamma rays and localizes in the abnormal thyroid tissue,
only the tumor is typically destroyed, generally sparing normal tissue and the
adjacent parathyroid tissue. After treatment, thyroid function returns to normal
usually within 1 to 3 months (however, in rare cases, it can take as long as 6
months).
Because parathyroid and normal thyroid tissue is spared, cats do not have calcium and
phosphorous regulation problems, nor do they typically require thyroid hormone
supplementation. General anesthesia is not required for 131 I therapy hence,
eliminating a major risk factor for the geriatric cat.
Will this treatment cure my cat's hyperthyroidism?
85-90% of the hyperthyroid cats treated with radioactive iodine will become normal
(euthyroid) within 1 to 3 months of therapy. 5-10% will have levels below normal
(hypothyroid) but less than 1 % will require oral thyroid hormone replacement medication,
and 3-4% will remain somewhat hyperthyroid after their initial dose. Cats with
persistent hyperthyroidism can be re-treated 3 months after their initial therapy.
Recent information suggests waiting 6 months if the cat is not showing hyperthyroid
related problems, some of these cats will become euthyroid during this time. Reasons
for failure to respond to the initial treatment may include prior treatment with
methimazole (Tapazole), or PTU, a very large thyroid mass, or a malignant thyroid
tumor rather than a benign tumor. Nearly all cats will be cured by a second treatment.
At 1 and 3 months after the treatment, a T4 blood test and kidney function tests
should be done by your veterinarian. The I month T4 test may be slightly high,
low or normal. During this first month your cat may be sluggish, sleep more and
eat less. Excessive shedding may also occur (rarely). These signs are all
related to correction of the thyroid hormone imbalance. The 3-month T4 test should
no longer be elevated. Any signs persisting after the T4 is normal are most likely
due to other medical problems that need to be identified and treated by your veterinarian.
Relapse following successful radioactive iodine therapy is very rare (approximately 1 in 200).
What alternatives are there to treat hyperthyroidism?
Antithyroid drugs such as methimazole (Tapazole), or P11J are often prescribed as
a temporary treatment but only control the signs often disease (the tumor continues
to grow). Side effects of (Tapazole and PTU) are common (18.3%) and include anorexia,
vomiting, lethargy, excoriations, bleeding, hepatopathy, thrombocytopenia,
agranulocytosis, leukopenia, eosinophilia, lymphocytosis, positive ANA, and
positive direct antiglobulin test. These drugs may be helpful in stabilizing very
ill cats before having definitive treatment with radioiodine. Antithyroid drugs must
be discontinued for 1 week prior to radioiodine treatment because they interfere
with iodine absorption. Due to the risks of anesthesia and hypocalcaemia from
parathyroid loss, surgery for this disease is generally not recommended if 131 I
is available.
What arrangements will I need to make?
Please call to schedule an appointment for consultation and treatment
with Dr. Wackerbarth. Appointments generally are scheduled on Mondays and
Thursdays every 30 minutes from 8:00 A.M. to 12:30 P.M. A thorough
examination will be given, and laboratory tests will be reviewed and repeated
if necessary. This will assist in determining the dose of 131 I to be given.
If your cat is traveling by air, we will want him/her to arrive a day or two
prior to the treatment date so we can obtain the above information. We will give
you the phone number of a courier service, which will pick up and deliver your
cat to and from the airport. An additional fee will be charged by the courier
company.
Should my cat be tranquilized for travel?
Some extremely nervous cats should be sedated prior to a plane ride or a long
car ride. This should be decided on an individual basis by you and your veterinarian.
The drug which we use most often for this is diazepam.
Do I need to stop the antithyroid medications (Tapazole or PTU) prior to 131} treatment?
Yes. They should be discontinued at least 1 week before treatment. Exceptions
can be made if your cat has serious cardiac disease. If your cat can tolerate
being without these medications for longer, then discontinue them even sooner.
The antithyroid medications may decrease 131 I uptake by the abnorma1 thyroid
tissue, and therefore will decrease its effectiveness. So, the longer they can
be off these medications without compromising their health the better—but 1
week seems to be fine if that's all they can tolerate.
What does treatment involve?
There are no side effects, and there is no pain or anxiety associated with 131
I treatment. The delivery of radiation is targeted to the overactive thyroid gland(s),
the cat does not experience any radiation side effects at the normal therapy doses
used to treat hyperthyroidism. The medicine is given as a subcutaneous injection,
usually on the day the cat is admitted to the clinic.
During their hospitalization, cats are housed in individual enclosures (30" x 30" x 24")
in an isolation room in the clinic. Fresh food and water are available at all times.
Please inform us of any likes or dislikes or special dietary needs that your cat may
have, so we can make their stay as comfortable as possible.
Is it possible that my cat is not a good candidate for radioiodine treatment?
To be candidates for radioactive iodine therapy, I request that all cats have screening
laboratory work (CBC, Chemistry profile and urinalysis) performed by the referring
veterinarian within one month of the treatment date, Cats with significant heart
disease should be accompanied by the appropriate diagnostics, It is important for
me to get copies of this labwork before your cat comes for treatment. Please have
your veterinarian fax or mail them.
If your cat has significant kidney failure, advanced heart failure or a malignant
cancer, we may be unable to make your cat better by treating the hyperthroidism and
your cat may not be a good candidate for treatment.
How long will my cat be in the hospital?
Most cats are in the hospital for 2 to 3 days, depending on the dose of 131
I administered and the excretion rate of the iodine. Cats having high thyroid
levels or very large thyroid tumors usually require larger iodine doses and may
have to stay in the hospital longer. Once admitted for therapy, your cat cannot
be discharged until its radiation exposure rate is at or below the level determined
by the state.
May I visit my cat while it's in the hospital?
No; unfortunately, clients are not permitted in the radiation ward. Toys or
blankets from home are also not permitted because they would become contaminated and
create more radioactive waste to be disposed of. However, you may send your cat's
favorite food or snacks, especially if it is a fussy eater.
How will I find out about my cat's condition while it's in the hospital?
You may call us for regular reports, preferably after 11 AM. Of course we will
call you to discuss any problems or complications, should they occur.
When my cat is ready to come home, what do I have to do?
Dr. Wackerbarth will advise you when the anticipated discharge date will be.
Please call after 10 A.M. that day to confirm that your cat has reached the
discharge level. If you are driving, we will set up a date and approximate
discharge time. If your cat will be traveling by plane, Dr. Wackerbarth will
inform you at the initial exam when the anticipated discharge day will be.
You will need to arrange the courier and the return flight. Charges for airfare
and courier service will be taken care of by you.
What precautions must I take when my cat comes home?
For the first two weeks upon returning home:
- Keep your cat indoors or under direct supervision or a leash if outside.
The concern is that you not allow your cat to expose other people if they are a
roamer. They will not contaminate the earth nor are their immune systems
compromised.
- We advise dose contact (closer than 1 foot) should be limited to one hour
per day. The dose you are exposed to is extremely low and will have no medical
consequences. We are attempting to minimize your lifetime cumulative exposure.
- Use a dumpable and flushable litter, dean the box 1-2 times per day and
flush the waste down the toilet. If you are on a septic system you may not
want to flush the sand type (non-biodegradable) litter down your septic system.
Place waste in a plastic bag (bread or vegetable bag) then place the bag of
waste into a container (5 gallon paint bucket) with a lid and store it out
of the way (garage, shop etc.) for 80 days, then discard into regular trash.
Do not put the litter into the trash prior to 80 days as it may set off
radiation detectors which would result in a significant fine to you. Sand
like clumpable litters are mandatory. ALL these litters clump up and allow
complete removal of urine while eliminating the chance of self-contamination
with 131 I in the litter box.
- Wash your hands carefully after handling your cat, its food dishes or
litter pan.
- Do not allow children or pregnant women to have contact with your cat.
- We advise you against sleeping with your cat, again our attempt is to
minimize your lifetime cumulative exposure.
- Do not allow your cat to sleep with family members.
These precautions seem like my cat is hazardous to me. How dangerous is it?
The amount of radiation remaining in your cat is extremely low. In fact, if your
cat were a person it would receive up to 33 mCi of 131 I and would have gone home
the same day treatment was given with none of the restrictions your cat has. The
amount of radiation you might receive would be equivalent to the radiation
received when you fly round trip across the country.
What precautions do I need to take for my other pets?
The amount of 131 I that your other pets will receive by contact with your
cat or by using its litter pan is negligible; you don't need to quarantine
your cat from other pets. The difference between limiting your exposure
and not limiting your other animals exposure is based on their shorter
lifespan of an animal thus not having decades of cumulative exposure.
Also their opportunity for exposure is minimal. They do not fly (less
atmospheric filtration) have routine x-rays or have some occupational
exposure.
How much will this treatment cost?
Treatment with 131 I, including hospitalization, nursing care, radioiodine
treatment and radioactive waste disposal costs $750.00. This does not include the
higher doses of radioiodine used for malignant thyroid tumors (less than 1%) or
additional care and/or medications your cat may require for other problems. The
$750.00 treatment fee will need to be paid when the cat is left for treatment.
I will need to examine the cat the day of scheduled therapy. At that time,
I will review their laboratory results (Chemistry screen, CBC, T4 and
complete urinalysis within one month of Iodine 131 therapy). Your
veterinarian will provide these. If they appear to be a good candidate for 131 I,
their dose will be determined and ordered for delivery on their scheduled treatment
day. This initial pretreatment examination will be $50.00.
Where is the location?
The Feline Hyperthyroid Treatment Center shares the facilities with Cats
Exclusive Veterinary Center, which is located at 19203 Aurora Avenue North,
Shoreline, W A 98133. Parking is on the front, side and rear of the building.
Enter the front door (Cats Exclusive) and we will take care of the rest.
From 1-5:
North or South, take the 175th Street exit (#176). At the exit stoplight turn
west on 175th (right if exiting from 1-5 South, left if exiting from 1-5 North).
Go approximately 1/2 mile to Aurora Avenue North, and turn right (north) at the
light. We are 1 mile north on the left (west) side of Aurora Avenue North (Highway 99)
directly past the Park and Ride.
There is a light at 192nd and Aurora Avenue, get in the left hand turn lane and
turn left then into our driveway on the right hand side.
From Highway 99:
North from Seattle to 192nd on the left side, just beyond the Shoreline
Park and Ride (the next intersection past Sky Nursery).
South from Everett past the Snohomish-King County line (near Costco) about
12 blocks down to 192nd (at the bottom of a slight dip) and turn right into
our parking lot (we are on the right side or west side of the street).
From the Edmonds-Kingston Ferry:
Exit the ferry and cross the railroad tracks and take a right on Edmonds
Way (first light). Follow Edmonds Way up the hill approximately 2.5 miles
until you come to the Highway 99 South exit. Go right onto the exit to the
stop sign then go right again onto Highway 99 (going south}. We are 12 blocks
south on Highway 99 on your right side (west).
19203 Aurora Avenue North * Shoreline, Washington 98133
206.546.1243 * 206.546.5758 Fax
5506 Pacific Avenue * Tacoma, Washington 98408
253.471.9200 * 253.471.9222 Fax
www.felinehtc.com
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