Northern California Veterinary Specialists, Inc.

Thank you for choosing Northern California Veterinary Specialists, Inc. to perform your pet’s radioiodine treatment.

Radioiodine treatment
It is considered the best treatment for feline hyperthyroidism because it is very safe and stress-free, and does not damage the normal thyroid tissue. Radioiodine is rapidly absorbed by the abnormal thyroid tissue like natural iodine (such as that present in table salt). Thyroid tissue is the only tissue in the body that uses an appreciable amount of iodine, so the treatment is very specific for thyroid tissue. The radioiodine emits radiation which selectively destroys the tumor while leaving normal tissue undamaged. Thyroid function typically returns to normal in 1-3 months. It is a single dose treatment. Anesthesia or incisions are not required. There is no risk of damage to the parathyroid glands, which reside within the thyroid tissue and maintain your cat's calcium balance. These glands are frequently damaged during surgery for hyperthyroidism, which may result in prolonged hospitalization and life-threatening seizures.
At our hospital, the treatment success rate is 98%. Less than 2% of treated cats require a second treatment. Virtually 100% of those cats respond completely. At NCVS, each patient is thoroughly evaluated and screened prior to treatment by our Board Certified Internist/Oncologist to make sure radioiodine therapy is the best treatment choice.

Your First Visit at NCVS
At NCVS we will perform a thorough physical exam of your pet and take a complete medical history. We will need a copy of all medical records for review. You can bring them with you, or have your referring doctor FAX or mail them. We will discuss any other relevant health problems with you prior to treatment. If your cat will be admitted for therapy at the first visit, as most of our patients are, we will ask you to bring enough of his usual food to last for 3-5 days, if he is on a special diet. We don't want to upset him by changing his diet while he stays with us. If your kitty is not a picky eater, you don’t need to bring any food, as we stock many, many favorite cat foods. Please also bring any medications your cat is taking, so we can review them and decide if we want to continue them during boarding. Tapazole® (methimazole) can be stopped any time after the tapazole trial is completed (please see). It is not true that Tapazole® (methimazole) must be stopped 2 weeks prior to radioiodine therapy. This is out dated information extrapolated from human medicine and is not pertinent to cats. We frequently continue tapazole therapy up until the date of treatment, so that patients do not experience anxiety and hyperactivity and have a more pleasant boarding experience. We are happy to help you decide when to discontinue Tapazole® therapy prior to your appointment. This is a judgment call based on your individual cat’s health and symptoms.
You can also bring a small toy or other favorite item for him to sleep with, but we cannot return this to you. Unfortunately, due to space constraints required for the storage of potentially radioactive/contaminated items we cannot accept large beds, entire blankets, or other large items.

Pretreatment screening
Some tests will be required to make sure your cat’s overall health is good and that she is a good candidate for treatment. These include a routine complete blood count, chemistry panel, and urinalysis. These tests will probably have been done by your referring veterinarian, and we will not need to repeat any tests that were normal within an acceptable time frame.
Cats are required to be up-to date on vaccinations for upper respiratory viruses, or be from a completely closed indoor home environment if you do not wish to vaccinate your cat. After your pet is examined, and, only if necessary, other tests such as a cardiac and/or abdominal ultrasound evaluation will be recommended. We do not recommend routine echocardiography as part of our usual patient evaluation unless clinically indicated, i.e., abnormal cardiac physical exam, heart rate >220, severe heart murmurs, difficulty breathing, and/or severe hypertension (indirect Doppler blood pressure measurement >200mm/hg). Echocardiography has not been shown to be useful in the management of feline hyperthyroidism in subclinical patients prior to radioiodine therapy, and can considerably add to the expense of treatment. Less than 10% of the pretreatment cardiac abnormalities found in hyperthyroid cats are considered clinically relevant and in no instance affect the decision to provide treatment. Most cats that have hyperthyroid cardiac disease will have resolution after treatment without further intervention.
Hyperthyroidism can mask pre-existing kidney disease by artificially improving kidney function. This happens because hyperthyroidism increases blood pressure through the kidneys (hypertension), and increases blood flow to the kidneys. These mechanisms, along with some poorly understood hormonal factors, result in a false improvement in kidney function. Unfortunately, when these false ‘props’ are removed when hyperthyroidism is cured, we discover that some patient’s kidney function is not as good as we thought. We want to make sure your cat will have adequate function after treatment, although foregoing treatment will result in on-going kidney damage. For this reason, we ask that your cat be treated with the anti-thyroid drug, Tapazole® (methimazole), until the thyroid level is less than 2.5 µg/dL. Once this value is achieved, the kidney values should be checked. If they are within acceptably normal limits, your cat should be a good candidate for radioiodine therapy. We are happy to help manage your cat's medication to help stabilize him and get him ready for treatment. If your cat cannot be medicated, or does not tolerate Tapazole®, or cannot be stabilized on a reasonable dosage of medication, we can still treat him, but we will take special measures to minimize the risk that kidney problems will surface, such as giving you specific management instructions after treatment. Since hyperthyroidism causes ongoing kidney damage while masking true kidney function, it is important that these steps be followed when possible. Please note: radioiodine therapy does not cause kidney disease; it unmasks the true kidney function.

Thyroid scan
Before treatment with radioiodine, a thyroid scan is performed using a low energy radioisotope (technetium pertechnetate).Click here for more information
The scan will confirm the diagnosis, identify the number of abnormal thyroid lobes, show functional activity, and the presence of ectopic thyroid tissue. The scan allows us to determine whether the lesions are most likely benign or potentially malignant (only about 2-5% of all hyperthyroid cats have thyroid cancer). The thyroid scan provides a very critical piece of information to determine the individual dose of radioiodine required for effective treatment for each cat. The isotope is given as a quick subcutaneous injection.

The treatment procedure
The treatment is very simple for your cat. The calculated dose of radioiodine is given as a subcutaneous injection, just like a vaccine. There are no side-effects from the injection.1 It does not cause any vomiting, diarrhea, or hair loss, since the entire dose is absorbed by the abnormal thyroid tissue, and only a very small dose of radioactivity is required. We have never seen a case of “vaccine induced” (injection site fibrosarcoma) after radioiodine therapy.
At NCVS each cat receives an individual treatment dose, based on the physical exam, lab work, thyroid scan, and possibly other factors. These data provide an objective measure of the severity of the thyroid disease, then the treatment doses of radioiodine are individually adjusted. The thyroid scans shown below demonstrated dramatic difference in size distribution of hyperfunctional thyroid tissue identified as bright spots of different size and intensity. 

Would you think it would be medically effective to treat these cats (thyroid scans shown above) with equal doses of radioiodine as other treatment centers advertise? If the cat did not respond to the first treatment, how much more iodine should be given? This could not be determined without a thyroid scan.


Hospitalization after treatment
Once admitted, your cat cannot be discharged until his/her radiation emission rate is at the legal, safe limit. State laws require us to board your cat after the treatment until his radioactivity in the thyroid tissue and excreta (urine and feces) drops below a certain level. This is for the safety of humans who may contact your cat, but is not an issue for your other pets. We begin checking the level about 3 days after treatment. Most cats are hospitalized from 5-7 days, depending on the dose of radioiodine administered and the excretion rate of the iodine. Because we know your cat is a member of your family and you will want them as close to you as possible once they are home, we take precautions to make sure your cat is safe to be released to you. This focus on your safety may require that your cat stay with us for a longer period of time than other centers advertise. When your cat is discharged earlier than we recommend, she is simply more radioactive when you take her home.
While your cat stays with us no visitation is allowed because of the radiation safety regulations. Unfortunately, state law does not allow you to visit your cat during the boarding period, but we will do every thing possible to make sure your cat has a pleasant experience. Cats are cared for in a climate controlled cats only room. The day length is regulated by an automatic timer, and we play the radio softly (cats seem to like classical music or talk radio the best). We will call you every other day to tell you how he is doing, but you may call us more frequently if you like. We will call you the first day your cat is ready to go home, and set up a discharge appointment for you.

After your cat goes home
After your cat goes home, you will need to follow some safety precautions for the first 2 weeks. We will give you a copy of the instructions at your first visit. These guidelines mainly cover how much direct physical contact you can have with your cat in the first 2 weeks post-treatment, and how to dispose of cat litter. These guidelines are mandated by the state to prevent radiation exposure to people. Your cat will be slightly radioactive when he goes home, but there is no health hazard to people if the guidelines are followed. If you follow the instructions, your radiation exposure is equal to a cross-country airplane flight.
When your cat returns home, he will slowly start to return to his pre-hyperthyroid state. If he lost weight as a result of being hyperthyroid, it may take a while for him to return to his original weight. If at any time after treatment, you are concerned about your cat, please contact us. We will work closely with
your referring veterinarian and follow your cat’s status post treatment. To evaluate your cat post-therapy, you will be asked to have blood work checked at 1, 3, 6, and 12 months after treatment. About one month after treatment, your cat should have a physical examination. Blood should be drawn for a thyroid level (T4 test) and kidney tests (BUN and creatinine). You can have your referring doctor do this for you, or we can do it, as you wish. Please make sure we receive the results, so we can discuss them with you.
Optimally, your cat should have a T4 value <2.5 µg/dL with acceptable kidney function. About 30% of all treated cats will have a subnormal screening T4 value the rest of their lives, yet be completely normal Click here for more information on post-treatment HYPOthyroidism. You will also receive a follow up survey letter from us after your cat has completed the treatment program. Your answers to our survey will help us provide the best hyperthyroid treatment program possible.

During the first month after treatment
You should gradually notice the symptoms of hyperthyroidism disappearing. Many cats begin eating and drinking less as their thyroid function normalizes. If you feel your cat isn't drinking or eating enough, or if you are worried about anything else, you should call us right away.

Treatment Goal
Our goal is to cure your cat's hyperthyroidism, and give you the longest, happiest time possible with your cat. Because you have made a commitment to providing the best possible health care for your cat, we would like to offer whatever assistance we can to help you. We invite you or your referring doctor to call for consultation if your cat has any problems, even if they are not related to hyperthyroidism. Dr. Van Vechten, in her capacity as a Board Certified Internist and Oncologist (cancer specialist), will always be willing to discuss your cat's health. It is her passion to treat and cure hyperthyroid cats.