Your cat has been placed on a waiting list at the WCVM Veterinary Medical Centre to receive radioactive iodine treatment for hyperthyroidism. To help prepare you for your cat’s trip and treatment, here are some of the most common questions that are asked about the WCVM's treatment program.

Q. When will my cat be treated?

Your name has been placed on our waiting list and you have been told an approximate date for treatment. We generally have a waiting list of from one to three months. The WCVM Veterinary Medical Centre is one of the only Canadian facilities offering radioactive iodine treatment for hyperthyroidism and as our treatment ward has a small capacity of only six cats, we may be unable to treat your cat immediately.

Q. What arrangements will I need to make?

The WCVM small animal medicine liaison will call you approximately two to three weeks before anticipated treatment to give you a date when clinicians would like to have your cat arrive at the hospital. The liaison will give you directions if you are travelling by car and assist you in making flight arrangements if your cat will arrive by airplane. The WCVM Veterinary Medical Centre has a very reliable courier service which will transport cats between the Saskatoon airport and the medical centre for treatment.

Q. Should my cat be tranquilized for travel?

Some very nervous cats should be sedated prior to a plane ride or long car trip to Saskatoon. This should be decided on an individual basis by your veterinarian. The drugs which we use most often for this purpose in hyperthyroid cats are phenobarbital, diazepam or gabapentin.

Q. My cat is on medication to control hyperthyroidism. Can it be treated?

Recent studies show that this medication does not interfere with the radioactive iodine treatment. If your veterinarian has prescribed anti-thyroid drugs like methimazole (Tapazole), continue to give it to your cat as directed. You can discontinue oral or topical medications one week before your pet is admitted to the VMC. If you feed Hill's Prescription Diet y/d to your cat, please discontinue using this type of pet food two weeks before your appointment.

Q. What will be done to my cat at the Veterinary Medical Centre?

When your cat arrives at the college, it will be welcomed, examined and placed in a comfortable cage with water and a litter box. Please fast your cat before arriving — this will allow us to conduct diagnostic tests that same day. We will then call you to let you know that your pet has arrived safely.

The next two or three days will be spent doing some tests to be certain that:

• your cat has hyperthyroidism
• is free from other serious disease
• will benefit from therapy.

Our clinicians will conduct blood tests, urine tests, chest X-rays, an ECG, and perhaps a heart ultrasound. If everything is as it should be, your cat will be scheduled for treatment three to five days after arrival at the WCVM Veterinary Medical Centre.

Cliniicans require that your cat be at the WCVM Veterinary Medical Centrefor tests during the first two to three days. As well, it is very important for your cat to stay in the hospital for a few days before treatment so the clinical team can assess how well your cat will settle down and eat for us.

Q. Is it possible that my cat is not a good candidate for treatment?

Our aim of treatment is to make your cat feel better and have a longer, happier life. We can cure hyperthyroidism, so if your cat’s symptoms are due to hyperthyroidism, the chances are that treatment will be successful.

If your cat has some other disease or a malignant (non-thyroid) cancer, we may be unable to make your cat feel better by treating its hyperthyroidism and your cat may therefore not be a good candidate for treatment. If our screening tests suggest that your cat is not a good candidate for radioactive iodine treatment, we will send your pet home to you.

Some of our tests will be directed at assessing the health of your cat’s heart. Hyperthyroidism can have very serious cardiac consequences and sometimes it is important to treat the heart specifically, as well as treating the hyperthyroidism.

Hyperthyroid cats have increased blood flow to their kidneys. When we successfully treat their hyperthyroidism, no matter which treatment we use, this abnormally increased blood flow returns to normal. When we treat hyperthyroidism in cats with concurrent kidney disease, we often see a noticeable deterioration in their kidney function and some cats may actually develop symptoms of kidney failure.

For this reason, whenever our physical examination findings or lab tests make us suspicious of kidney disease in a hyperthyroid cat that has been referred for radioiodine treatment, we recommend that the cat's hyperthyroidism be treated first with reversible anti-thyroid drugs (methimazole) for a few months. This will allow us to determine the extent to which kidney function will be compromised in your cat when we treat the hyperthyroidism with a permanent treatment such as radioactive iodine.

Q. What does the treatment involve?

One morning your cat will be moved to our isolation ward. This is a small ward in the same building as our Small Animal Clinic but it is separate from the clinic. Cats will be individually housed in large cages in this nice, quiet room and will have no contact with other cats during their hospitalization. Radiation safety regulations prohibit us from allowing owners and untrained students or staff to visit the room before or after treatment.

Your cat will receive a small precise volume of radioactive iodine orally or subcutaneously in the early afternoon. This injection is not painful and the entire treatment takes less than five minutes. There is no pain or anxiety associated with the treatment. We have not noticed any side effects in the cats treated in this manner.

Q. How long will my cat have to stay at the Veterinary Medical Centre?

Most cats stay at our hospital approximately 10 to 14 days. This includes two to four days before treatment and approximately five to 10 days after treatment. Radiation safety regulations mandate that we must keep cats until their level of radioactivity reaches an acceptable level.

We will use a Geiger counter to measure the amount of radioactivity left within your cat beginning five days after treatment with radioactive iodine. Once the degree of radioactivity measured over the thyroid gland has diminished to a certain level, we know that there is no longer any radioactive iodine being excreted in the urine or saliva so exposure to the cat should pose no risk to humans or other pets.

Q. How will I know how my cat is doing?

Initially, while your cat is in the regular ward, a small animal medicine student or clinician assigned to the case will call daily or every other day to update you. You will be called on the day of treatment and then get daily updates by the student who works in the hyperthyroid cat ward.

Rest assured that we will also call you immediately if your cat encounters any problems while at the college. Please be sure that your work and home telephone numbers are correct and current upon your cat’s admission to the hospital. Also, when the student from the hyperthyroid ward calls you the first time, try to let them know the best time of day to reach you.

Q. Who will take care of my cat?

We have three advanced veterinary students who have a special interest in old cats and have been hired to work in the ward. They do the feeding, cage cleaning, cuddling and grooming of your cat each day as well as administering any medication which is needed. In addition, a veterinarian will visit with the cats each day to play with them and examine any that are having problems.

Q. What will my cat be fed?

We normally feed a wide variety of canned and dry foods. If your cat has specific likes and dislikes or dietary needs, please let us know and perhaps send some food along with your cat.

Q. Can I send my cat’s favourite toys, a blanket or an article of my clothing?

You are welcome to send almost any items along that you feel would make your cat’s stay more pleasant. Unfortunately, however, we can not return anything that we put in the isolation ward with your cat due to the problem with radioactivity and regulations established by the radiation safety office.

Q. When my cat is ready to come home, what will I need to do?

You will get a phone call from the veterinary student or clinician who cares for your cat or from our liaison regarding arrangements to send your cat home. If you are driving, we will set up a date and approximate time.

If your cat is to return by airplane, you will need to book a convenient flight and inform us of the date, flight number, waybill number and the time that your cat will depart. We will contact our courier to ensure your cat is at the airport in a timely fashion.

Q. What is the cost and how will I pay?

The WCVM Veterinary Medical Centre prices hyperthyroid treatments on cats on a break-even basis. To receive a quote for the approximate cost of treatment (without complications) contact the Small Animal Clinic (306-966-7126).

If your cat has other concurrent problems (such as diabetes or heart failure) which require intensive therapy, the bill may be a little higher. Courier charges to and from the airport are not included in the quote. We ask that you give us a deposit of $800 at admission as well as the remaining charges at the time of discharge.

Q. Will I need to take any precautions once I get my cat home?

Your cat will not be discharged from our hospital until there is no risk of exposure to radioactive urine and saliva. We still suggest that for 10 days, please do the following: 

• confine your cat to your house
• clean the litter box while wearing gloves
• do not allow the cat to sleep in bed with you.

Other close contact is permitted. There is no risk to other pets in the household. If there is a pregnant woman in the household, we often recommend that we keep the cat at the WCVM medical centre for an additional seven days just to ensure absolute safety.

Q. How successful is this treatment?

Greater than 90 per cent of cats treated with radioactive iodine will be cured by a single dose. Your veterinarian should take a blood sample about two to four weeks after your cat returns home to confirm that treatment has been successful and to evaluate kidney function. Please send a copy of the blood test results to Prairie Diagnostic Services (PDS).

A small percentage of cats will not respond completely to this treatment. They will feel better and symptoms may disappear, but the thyroid hormone level is still high and these cats will relapse within months. Reasons for failure to respond to the initial treatment may include a very large thyroid mass or the presence of a malignant thyroid tumor instead of a benign one. These cats may be cured by a second treatment of a very high dose of radioactive iodine.

A few cats will become hypothyroid after treatment. These cats for some reason respond more completely to the low dose of iodine than is desirable. This is usually not an important clinical problem. Occasionally, however, there will be clinical signs such as weight gain, sluggishness and poor hair coat requiring treatment with thyroid hormone replacement (pills) — a drug therapy that may be required for the rest of your cat's life.

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This information is intended for veterinarians with questions regarding the referral of hyperthyroid cats for treatment with radioactive iodine (131l).

Cost

Please contact the WCVM Small Animal Clinic at 306-966-7126 and ask for a quote that details the approximate cost of treatment (without complications). If the cat has other concurrent problems that require intensive therapy (such as diabetes or heart failure), the bill will be higher. Courier charges to and from the airport are not included in the quote.

We ask clients to give us a deposit ($800) at the time their cat is admitted. We bill them for the remaining charges at the time of hospital discharge. We do not offer in-house credit arrangements or payment plans.

Anti-thyroid drugs

Studies show that methimazole (Tapazole) administration does not interfere with radioactive iodine treatment. If you feel that a cat would benefit from treatment with antithyroid medication prior to referral for radioactive iodine treatment, that is not a problem. Oral and topical medication can be discontinued one week before treatment. If the patient is being fed Hill's Prescription Diet y/d, please discontinue using this pet food two weeks before treatment. We will discontinue the anti-thyroid medication when the cat is admitted to this hospital (usually three to four days prior to the actual radioactive iodine treatment).

Q. What tests are conducted at the WCVM Veterinary Medical Centre?

All hyperthyroid cats that come to the WCVM Veterinary Medical Centre will have the following diagnostic tests performed:

• physical examination
• complete blood count (CBC)
• serum biochemistry profile
• resting T4
• electrocardiogram (ECG)
• chest radiographs
• blood pressure

Other studies (cardiac ultrasound, urine culture, abdominal ultrasound) may be performed if the attending clinician considers that the tests are warranted based on the patient's history, physical findings or initial testing results at an additional cost. 

Q. Who cares for the cat?

The cat is admitted to the hospital as a medical case and will be under the care of a Small Animal Medicine clinician. The cat will be examined and the appropriate diagnostic testing performed to make certain that the cat is a good candidate for radioactive iodine therapy.

If the cat is a suitable candidate for this therapy, then the radioactive iodine dose will be administered orally or subcutaneously and the cat will be moved to our special ward for radioactive hyperthyroid cats.

While staying in the special ward, the cat will be under the direct care of trained veterinary students who look after all of the cat's needs. The cats are cleaned, watered and fed twice a day and medications are administered as required. The students also find time to groom and pet the cats who appreciate this kind of attention.

The students immediately notify the clinician in charge of the ward if there are any medical problems with any of the cats. The students also call the owners at least once a day to let them know how their cats are doing after treatment. If there are problems with a cat while it is at the WCVM, the owners are notified immediately by the clinician in charge.

Most hyperthyroid cats are older (average age 12 years) and owners are concerned that they won't do well during their period of hospitalization. We have treated approximately 450 cats over the past years and our experience is that these cats do very well in our hospital.

That being said, it is very important to us that these cats eat while they are staying at the WCVM hospital. We encourage owners to send along a special or favourite diet if their cat is very nervous or is a picky eater. If we can not convince a cat to eat in the days preceding the planned treatment, we will not treat it and we will send it home.

This is one reason (in addition to the pre-treatment testing) that we request cats arrive at our hospital two to four days before the planned treatment: we want the cats to get a chance to acclimatize, relax and start to eat in our hospital.

Arranging referral to the WCVM

Cats are treated in "batches" to minimize the costs associated with the treatment, care and housing of the cats. We can treat five to six cats at a time.

The WCVM small animal medicine liaison will be able to give you an estimate of where a cat is on the waiting list and how long it is likely to be before the cat can be accepted for treatment.

To place a cat on the waiting list, please submit an online medicine referral. We will then call the client directly two to three weeks prior to the scheduled treatment to arrange hospital admission.

Medical considerations

When the cat is sent to the WCVM for treatment, please forward a brief summary of the cat's medical history and the results of any recent laboratory tests. You can send this information along with the cat or please fax it to 306-966-7156. The summary should include an assessment of renal function (urea or BUN, creatinine, urine specific gravity), a serum T4, and the details of any treatment administered.

We will not accept "sick" cats for treatment. Medically unstable cats have a much greater likelihood of complications compared with stable cats. The referring veterinarian must ensure that the cat is fit for travel (if it has to be transported by plane or driven to the hospital) and that it can withstand the stress of examination and hospitalization.

Hyperthyroidism and chronic renal failure are both common disorders in older cats. We know that GFR decreases with successful treatment of hyperthyroidism in most cats regardless of the therapy used (medical, surgical, radioactive iodine). In cats with pre-existing renal dysfunction, the deterioration in GFR that accompanied resolution of hyperthyroidism can result in symptomatic renal failure.

For this reason we ask that referring veterinarians try to carefully evaluate kidney function in cats before sending them here for radioactive iodine treatment. If there is evidence of pre-existing significant kidney dysfunction we recommend that treatment with a permanent treatment such as radioactive iodine be delayed while medical treatment of the hyperthyroidism is attempted with reversible antithyroid drugs (methimazole) for a few months.

If renal function is stable when the cat is maintained at a euthyroid state for one to two months, then it is a good candidate for radioactive iodine therapy.

The treatment process

On the morning of treatment, the cat will be moved to our isolation ward. This small ward, which contains large cages, is located in a separate area of the Small Animal Clinic building. It is a nice, quiet room. The cats are housed individually and have no contact with other cats during their hospitalization.

Each cat receives a fixed low dose of radioactive iodine orally or subcutaneously. If we have reason to suspect thyroid carcinoma instead of adenomatous hyperplasia in a cat (lung metastases visible on thoracic radiographs or failure to respond to initial treatment), then we treat with a high dose intended to ablate all thyroid tissue. There is no pain or anxiety associated with the treatment and we have not noticed any side effects in the treated cats.

Length of stay

Most cats stay at the WCVM Veterinary Medical Centre for approximately 10 to 14 days. This includes two to four days before treatment and approximately five to 10 days after treatment.

Radiation safety regulations mandate that we must keep cats until their level of radioactivity reaches an acceptable level. We will use a Geiger counter to measure the amount of radioactivity left within each cat beginning seven days after treatment with radioactive iodine. Once the degree of radioactivity measured over the thyroid gland has diminished to a certain level, we know that there is no longer any radioactive iodine being excreted in the urine or saliva. As a result, exposure to the cat should pose no risk to humans or other pets.

When owners take their cat home, they will be asked to follow radiation safety guidelines for two weeks (wearing gloves to change the litter box, not sleeping with the cat). If the owners feel that they are unable to follow those guidelines or they feel uneasy with the very low potential for exposure, we are willing to keep the cats for that additional one-week period (at boarding cost).

Treatment outcome

Greater than 90 per cent of cats treated with radioactive iodine will be cured by a single dose. We ask that you re-evaluate the cat about two to four weeks after hospital discharge to confirm that treatment has been successful (measure T4) and to evaluate kidney function. Please send a copy of the blood test results to Prairie Diagnostic Services (PDS).

A small percentage of cats (less than five per cent) will not respond completely to this treatment. They will feel better and symptoms may disappear, but the thyroid hormone level is still high and these cats will relapse within months. Reasons for failure to respond to the initial treatment may include a very large thyroid mass or the presence of a malignant thyroid tumor instead of a benign one. These cats may be cured by a second treatment of a very high dose of radioactive iodine.

A few cats will become hypothyroid after treatment. For some reason, these cats respond more completely to the low dose of iodine than is desirable. This is usually not an important clinical problem and does not result in any symptoms. Occasionally, however, there will be clinical signs such as weight gain, sluggishness and poor hair coat requiring treatment with thyroid hormone replacement (pills) — perhaps for the rest of the cat's life.

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