Hyperthyroidism is a disease caused by excess amounts of circulating thyroid hormone in the bloodstream. This is a common medical condition in middle-aged to geriatric cats, and it usually results from one or more benign tumors (adenoma or adenomatous hyperplasia) of the thyroid gland. Carcinoma (cancer) is a very rare cause of hyperthyroidism in cats, at least in the initial stages of the disease.

Excess thyroid hormone accelerates most bodily processes and gradually causes the clinical signs that are apparent to most owners. The most consistent finding is weight loss secondary to the hyperthyroid cat’s increased rate of metabolism. Most cats try to compensate for their weight loss and increased rate of metabolism by eating more (increased appetite). In fact, some of these cats have a ravenous appetite and will eat literally anything in sight! However, despite the increased food intake, most cats lose weight. While the weight loss may happen quickly, it may also be so gradual that some owners will not even realize it has occurred. Other signs of hyperthyroidism may include anxiety or nervousness, a rapid, pounding heart rate, muscle weakness, vomiting, diarrhea, increased thirst or urination, heat intolerance (panting), and an unkempt hair coat. Over time, untreated or poorly controlled hyperthyroidism leads to deleterious effects on many of the cat's internal organs. Heart failure, kidney and liver disease, muscle wasting, chronic emaciation, and/or severe metabolic dysfunction can develop, ultimately leading to death.

Fortunately, hyperthyroidism is both familiar to veterinarians and relatively easy to diagnose. The veterinarian can diagnose hyperthyroidism based on the cat's history, physical examination abnormalities, and results of routine laboratory tests and thyroid hormone tests. Most cats have one or two palpable, enlarged thyroid tumors (nodule[s]) in their ventral neck area, an important finding for making the diagnosis. Almost all cats will also have clearly high serum thyroid hormone levels, diagnostic for hyperthyroid. in those cats in which the thyroid tumor cannot be palpated or that have only borderline high thyroid concentrations, thyroid imaging (scanning) can be extremely useful in confirming hyperthyroidism.

Cat Thyroid Storm: A Hyperthyroid Cat, Before Radioiodine Treatment Click here to watch the video

Formerly Hyperthyroid Cat, Now Cured of Hyperthyroidism With Radioiodine Click here to watch the video

Hyperthyroidism can be treated medically, surgically, or with radioiodine. Medical treatment consists of administering methimazole (Tapazole™ or Felimazole™) one to three times per day. Methimazole treatment usually controls the signs of hyperthyroidism, but it is not a cure (i.e., the drug will block thyroid hormone secretion but will not remove or destroy the thyroid tumor). The drug must be given for the rest of the cat's life. Surgery cures the hyperthyroid condition by removing part or all of the thyroid gland. Radioiodine (radioactive iodine; I-131) also cures hyperthyroidism. The procedure for this treatment is simple; it is a single subcutaneous injection of a radioiodine, given much like a routine vaccine.

Medical therapy works in most cats, but there are 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 and vomiting) are common, and a few cats develop serious adverse reactions to the medication (blood or liver problems). Because of these side effects, it is necessary to periodically monitor the cat’s condition with blood tests. Finally, some owners may not want to have to medicate their cat daily for the rest of his or her life, especially if the cat is young or only middle-aged. It is important to remember that while medical therapy "blocks" production of thyroid hormone secretion, the thyroid tumor(s) will still grow and enlarge over time. Some of these thyroid tumors will also transform from a benign to a cancerous thyroid over time (months to years). In many cats treated with long-term medical therapy, the signs of hyperthyroidism recur when the tumor becomes so large that the medication can no longer effectively block thyroid hormone secretion.

Surgery is generally an effective treatment for hyperthyroidism, but it has disadvantages in many cats. Many cats with hyperthyroidism have heart problems and thus have more risks with anesthesia. There is also a considerable risk that there will be damage to the parathyroid glands (4 little glands located within or adjacent to the thyroid) during thyroid surgery, resulting in hypocalcemia (low blood calcium). This complication can be life-threatening and results in substantial additional hospitalization costs. After surgery, some cats develop hypothyroidism and require treatment with thyroid hormone pills for a period. Finally, there is a considerable risk that the surgery will not completely cure the hyperthyroidism, or that the condition will recur (i.e., radioiodine has a much smaller chance for recurrence)

Radioiodine therapy has some distinct advantages over medical or surgical treatment, and virtually all authorities consider it to be the treatment of choice for hyperthyroidism. With radioiodine, there is no need for anesthesia and the risk of postoperative hypocalcemia is eliminated. Methimazole (Tapazole™ or Felimazole™) treatment is not needed. The major draw back is that after receiving radioiodine, the cat must be kept in the hospital for a period (usually 3 to 5 days). Overall, radioiodine provides a simple, effective, and safe cure for cats with hyperthyroidism, regardless of age.

Normal thyroid function requires oral intake of the element iodine (iodine is a normal part of both human and cat diets and is commonly added to salt). Once ingested, iodine is taken up by the thyroid gland, where the iodine becomes incorporated into thyroid hormone. Radioiodine (radioactive iodine; I-131) is a radioactive form of stable iodine. In its radioactive state, it naturally decays, giving off two types of radiation: gamma rays (similar to X-rays) and beta particles (electrons). The half-life of I-131 is 8 days. In other words, one-half of the radioiodine decays every 8 days.

When a cat receives radioactive iodine, the thyroid tumor tissue takes up the radioiodine just as readily as normal, nonradioactive iodine (the kind in iodized salt). All thyroid tumor tissue will take up the radioiodine in this fashion, no matter where in the body it is located. This is an important feature of radioiodine therapy because up to a third of hyperthyroid cats have thyroid tumors in the chest cavity, where surgical removal is not feasible. Once the thyroid tumor tissue has taken up the radioiodine, the radioiodine emits radiation, destroying the overactive thyroid tumor cells.

Because the hyperactive thyroid tumor suppresses the function of any normal thyroid tissue, the normal cells do not concentrate any of the radioiodine. Because almost all hyperthyroid cats have some residual, normal thyroid tissue, this means that cats rarely develop an underactive thyroid gland (hypothyroidism) after radioiodine therapy. These spared normal thyroid cells then can “turn back on,” and make normal amounts of thyroid hormone after the radioiodine has destroyed all of the tumorous tissue.

After treatment, the residual (normal) thyroid tissue resumes full function within 1 to 3 months. On average, 98% of all hyperthyroid cats treated with radioiodine are permanently and safely cured with a single injection! As an added benefit, radioiodine poses no risk to the parathyroid glands, the four small glands located adjacent to the thyroid gland, which are extremely important for maintaining normal calcium levels. Therefore, hypocalcemia (low blood calcium) secondary to parathyroid damage never occurs after treatment with radioiodine. This is markedly different from surgical treatment, which very commonly damages the parathyroid lands, causing life-threatening hypocalcemia.

Dr. Mark E. Peterson Interviewed About Hyperthyroidism in Cats Click here to watch the video

How Does Radioactive Iodine Work in a Cat with Hyperthyroidism? Click here to watch the video

Hyperthyroid cats of any age can be successfully treated with radioiodine, as long as they have no other life-threatening medical conditions. In order to rule out any additional medical conditions, your veterinarian needs to perform a number of screening tests before you schedule an appointment at Hypurrcat for the radioiodine treatment.

Dr. Peterson was the first veterinarian to develop this procedure for use in hyperthyroid cats. He has over 30 years of experience successfully administering radioiodine therapy to cats. It is not a new or experimental treatment; Dr. Peterson has treated over 10,000 hyperthyroid cats in his long career.

Please ask your veterinarian to send us (via fax or e-mail) the results of your cat's history, physical examination, x-rays or ultrasound reports, and recent blood work (e.g., complete blood count [CBC], serum biochemical profile, urinalysis, and serum thyroid hormone tests) so that Dr. Peterson can evaluate whether your cat is a good candidate for treatment. We recommend that these blood tests be done within 30 days of your appointment for radioiodine treatment. If hyperthyroidism is confimed and no other life-threatening medical conditions are identified, we will then schedule an appointment for your cat's treatment. Please call us to schedule an appointment.

If your cat has been treated with methimazole (Tapazole™ or Felimazole™) for longer than 3 months, you should stop the medication for 3 to 5 days and repeat the serum thyroid hormone tests. We need a current serum T4 reading off methimazole to help determine the correct dose of radioiodine to administer to your cat. If stopping the medicine is not possible because of severe hyperthyroidism, we use thyroid imaging to help determine your cat’s proper radioiodine dose.

In recently diagnosed hyperthyroid cats receiving methimazole, the drug is generally discontinued one week before treatment with radioiodine but you do not need to repeat your cat’s thyroid test. However, in some cats (especially those with a concurrent illness), Dr. Peterson may want you to continue methimazole treatment up until the day your cat is admitted for radioiodine therapy.

Most other drugs that your cat may be receiving are fine, but please check with our office to make sure that these medications will not interfere with the radioiodine treatment. You should feed your cat normally the week before admission to the hospital.

Cat owners can feel both confident and worry-free about placing their cat in the care of Hypurrcat’s staff. As cat owners ourselves, we know boarding your cat for radioiodine treatment is typically much more stressful to the owner than to the cat. That's why we've gone to every extent to ensure you have peace of mind that your cat will be safe, loved, and have a good time while in our care.

Cats, especially those hospitalized for more than a day or two, need stimulation and recreation to maintain their mental health. This is often referred to as “environmental enrichment” or “environmental enhancements.” Examples include an environment with perches, hiding boxes, beds, and toys, as well as “safe” places to sleep, eat, and use the litter box. Daily positive interaction with their human caretakers also benefits hospitalized cats. Spending a few minutes each day petting, brushing, and playing with the cats, as well as speaking to them in a soft, calming voice, provides comfort to the cats.

At Hypurrcat, we know that cats do much better during their hospitalization when boarded in large condos and provided with live entertainment. Each of our cat condos has a separate bathroom (with litter box), a perch that allows the cat to get above the action, a hiding box, as well as their own bed and toys. Our Hypurrcat treatment facilities are strictly “For Cats Only!” We have no dogs barking in the background; the cats hear only soft music played throughout the day. To help keep cats entertained during their stay at Hypurrcat, we offer a wide selection of cat videos that are shown on a widescreen TV within the treatment room. Furthermore, we feature live entertainment.

At our NYC Hypurrcat facility, the cats enjoy 40 x 27 x 25 inch condos and a great window view of the back courtyard where we have multiple bird feeders set up. The cats can observe the birds (and squirrels) feeding just a few yards away.

At our Westchester Hypurrcat facility, we are often able to link two of these condos together in order to give each cat his or her own private double-sized condo. The cats can also view two gerbil habitats in front of their condos, where the gerbils scurry through habitrails and run on exercise wheels.

Tour of the Luxury Boarding Facilities at the Hypurrcat Spa Click here to watch the video

A diagnostic imaging procedure called thyroid scintigraphy or thyroid scanning has long been considered the “gold standard” in the diagnosis of feline hyperthyroidism. After administering a short-acting radioactive isotope (radionuclide) that concentrates in thyroid tissue, thyroid imaging directly visualizes the normal thyroid gland, as well as the small tumor(s) responsible for hyperthyroidism in cats. Because this procedure utilizes the physiology of the thyroid gland to create an image, thyroid imaging is so sensitive that it can actually demonstrate the presence of hyperfunctional thyroid tumors long before they become clinically significant or result in laboratory value abnormalities. Unfortunately, because of the costly nuclear medicine equipment and radioisotopes needed, thyroid imaging is not generally performed at most radioiodine treatment facilities.

At Hypurrcat, we have the nuclear medicine imaging equipment and special licensing required to perform thyroid scintigraphy. This allows us to readily perform thyroid imaging in any cat that needs it to accurately confirm the diagnosis of hyperthyroidism. This is especially helpful in those cats with borderline high T4 concentrations but no palpable thyroid nodule.

At Hypurrcat, we individualize the I-131 dose administered to each hyperthyroid cat. Although Dr. Peterson has proven that tumor size can be accurately estimated by physical palpation of the thyroid gland in most cats, about a third of hyperthyroid cats have thyroid tumors located within the thoracic cavity and cannot be palpated.

Most of the hyperthyroid cats without palpable cervical nodules have thyroid tumors (adenoma or carcinomas) that have become extremely large. Because of the chronic effects of gravity on the progressively enlarging thyroid mass, these tumors migrate into the thoracic cavity. Other cats develop hyperthyroidism secondary to adenomas of ectopic, intrathoracic, thyroid tissue. Both of these situations render these thyroid tumors beyond the reach of palpation. In cats with a thyroid carcinoma, extension or metastasis to the thoracic cavity is common, so physical palpation alone will grossly underestimate the full extent of these malignant tumors.

At Hypurrcat, we recommend thyroid scintigraphy for all cats with suspected intrathoracic thyroid tumors (e.g., when the thyroid tumor is not easily palpable). We also perform thyroid imaging on all cats in which thyroid carcinoma is known or suspected. This allows us to calculate the proper dose needed to adequately treat cats with a large thyroid adenomas or carcinoma. Most radioiodine facilities are not licensed to treat cats with thyroid carcinoma with the large doses needed to cure these cats (i.e., up to 10 times the I-131 dose that typical cats with thyroid adenoma need). However, Dr. Peterson has successfully treated many cats with thyroid carcinoma over the last 30 years.

Preparing a Feline Patient for a Thyroid Scan by Injecting Radioactive Dye Click here to watch the video

Performing a Thyroid Scan on a Hyperthyroid Cat Click here to watch the video

Thyroid Tumors in Cats: Benign vs Malignant Click here to watch the video

Please bring your cat to the hospital in a carrier at the scheduled time. You should feed your cat that morning (fasting is not necessary).

Admission Day at The Hypurrcat Spa for Hyperthyroid Cats Click here to watch the video

When you arrive at our Hypurrcat facility on the admission day, you will first be asked to read and sign the form entitled "Owner Consent to Treat their Cat with Radioactive Iodine." If you wish, you may download this form, and fill out the required information prior to your cat's examination.

Once you have completed the required paperwork, you and your cat will meet with Dr. Mark Peterson, our board-certified veterinary endocrinologist. He will thoroughly examine your cat and review the medical records and tests performed by your regular veterinarian. He will also answer any questions you have concerning the treatment or long-term care. If your cat is judged to be a good candidate, we will treat your cat that day.

Admission Day at The Hypurrcat Spa for Hyperthyroid Cats Click here to watch the video

Once we determine your cat’s radioiodine dose, it is injected in a small volume (1-ml) under the skin (subcutaneously), exactly like a routine vaccination. There is absolutely no discomfort associated with this injection, and the entire procedure takes less than 1 minute.

Treating a Hyperthyroid Cat with Subcutaneous Injection of Radioiodine Click here to watch the video

Once your cat has been treated, he or she need do nothing else but sleep, eat, and play while the radiation within the body dissipates to safe levels. We like to "spoil" all our patients as much as safely permissible. During hospitalization, we provide favorite foods, diversions, and lots of "hands-on" care, brushing, and affection.

At Hypurrcat, we know that cats do much better during their hospitalization when boarded in large condos and provided with live entertainment. Each of our cat condos has a separate bathroom (with litter box), a perch and hiding box, as well as their own bed and toys. To help keep cats entertained during their stay at Hypurrcat, we offer a wide selection of cat videos that are shown on a widescreen TV within the treatment room. Furthermore, we feature live entertainment.

At our NYC Hypurrcat facility, the cats enjoy 40 x 27 x 25 inch condos and a great window view of the back courtyard where we have multiple bird feeders set up. The cats can observe the birds (and squirrels) feeding just a few yards away. At our Westchester Hypurrcat facility, we are often able to link two of these condos together in order to give each cat his or her own private double-sized condo. The cats can also view two gerbil habitats in front of their condos, where the gerbils scurry through habitrails and run on exercise wheels.

Your cat will be monitored closely while in our care. Our attentive staff frequently monitors and records your cat’s hydration level, appetite, thirst, urinations, defecations, and general attitude. The cats are fed two to three times daily by one of our Hypurrcat care specialists and are monitored daily by Dr. Peterson during their stay.

Since each cat's metabolism is slightly different, the length of stay varies and is determined by the remaining radioactivity in your cat’s thyroid gland. State and City law requires that a cat remain hospitalized until the radioactivity has dropped to a very low level. This usually takes 5 to 10 days (average, 6-7 days). We measure the radioactivity emitted by your cat’s thyroid every day during their hospitalization, and we contact you regarding discharge as soon as the radiation is at a safe level. We can also make arrangements for owners who wish to have their cat stay a longer period in our Hypurrcat facilities.

Before your cat is discharged, we will repeat the thyroid function tests to gauge the success of the treatment. We will also repeat the serum kidney and liver profiles to determine if any changes in these parameters have occurred following treatment. We will remain involved in your cat's recovery and will review the results of treatment with your veterinarian.

At Hypurrcat, we understand the special role the cat plays in the owner’s family. Our entire Hypurrcat team is committed to providing personal attention to the unique concerns of each individual cat and cat owner. We call or email each owner once or twice daily during their cats stay. We are always available to speak to an owner when their cat is being treated at Hypurrcat.

Almost all owners would like to visit their cat during their hospitalization, but they cannot because of the potential for radiation exposure during the first few days after treatment. That’s why we offer owners and veterinarians the ability to monitor their cats live over the Internet (even on a smartphone).

Both of our Hypurrcat facilities have private cameras installed in each of the cat condos. The web cams allow both the owner and referring veterinarian to check in on their cat, even though they cannot visit. When your cat is admitted, we will email you a “link” that you can open on your home or office computer (or smartphone) to monitor your cat live over the internet. You can share this link with friends and family so that everyone can participate in checking in on your cat!

Using the Hypurrcat Spa's Webcams to View Your Cat from Home Click here to watch the video

Once treated, cats cannot be removed from the Hypurrcat facility until the level of radioactivity has decreased to a safe level. The New York City and New York State Departments of Health and the Nuclear Regulatory Commission mandate this rule.

Yes, of course your cat will still be cared for! At our Hypurrcat facility in Bedford Hills, all of our staff members drive all-wheel drive or 4-wheel drive vehicles, enabling them to travel in very severe weather. Hypurrcat also has sleeping accommodations for its staff, so they can stay at the hospital if necessary. Inclement weather is less of a problem in NYC because our staff can easily either walk or take public transportation to the clinic.

There are almost no side effects from radioiodine treatment. Since the radioiodine is specific in its site of action (i.e., at the thyroid tumor), there is no hair loss or increase in skin pigmentation as may be seen with other forms of external radiation therapy (eg, LINAC or cobalt radiation). Once your cat is back at home with you, there may be a period of readjustment while your cat’s thyroid returns to normal function. Your cat may be quieter and less active than “normal” (recall that “normal” was hyperthyroid!). Because your cat's metabolic rate will return to normal after treatment, he or she may not need to eat as much food as before therapy. A change in voice may develop after treatment, but this is extremely rare. Rarely, a cat will develop hypothyroidism (underactive thyroid gland), which is easily controlled with thyroid hormone supplementation. Overall, side effects are extremely rare.

Radioactive iodine, despite its somewhat scary title, is considered the "gold standard" for safety and efficacy in treating hyperthyroid cats. The greatest risk is radiation exposure to the doctors and staff who work in the thyroid treatment facility on a long-term basis. However, with stringent safety regulations, protocols, and monitoring, this form of therapy is safe for both the cats and the caregivers!

Chronic kidney disease and hyperthyroidism often occur together because they are both common disorders in older cats. Hyperthyroidism tends to artificially increase the blood flow to the kidneys as well as the glomerular filtration rate (GFR). The GFR is a measure of how efficiently the kidney filters the blood. When it is artificially increased, it can mask renal insufficiency; blood tests on a hyperthyroid cat may appear normal despite mild to moderate kidney disease.

Treating hyperthyroidism restores the high serum T4 concentration to normal. This tends to lower kidney blood flow and GFR to normal or low levels, “worsening” kidney function tests. It is important to remember that treating hyperthyroidism itself does not cause chronic kidney disease; the kidney problem was already present before treatment. It was simply masked by the hyperthyroidism.

Chronic kidney disease is reported to be prevalent in 8% of cats >10 years of age and 15% of cats >15 years of age. In contrast, up to 30-40% of hyperthyroid cats have chronic kidney disease. This suggests that hyperthyroidism may be initiating or worsening the chronic kidney disease in these cats. If this is true, one should always try to correct the cat’s hyperthyroidism, even if the cat has known renal disease.

In addition, recent reports indicate that many untreated hyperthyroid cats develop proteinuria (excessive protein in the urine), This proteinuria resolves after successful treatment with radioiodine. In addition, high levels of retinol binding protein, a marker for renal damage, have also been shown to decrease significantly after radioiodine treatment. This too suggests that hyperthyroidism can cause reversible renal dysfunction.

Therefore, it appears that leaving a hyperthyroid cat untreated (or poorly regulated with methimazole) may be detrimental to long-term kidney function. However, treating and curing hyperthyroidism may help to preserve remaining kidney function.

Determining which untreated hyperthyroid cats have clinically significant underlying chronic kidney disease can sometimes be difficult. Methimazole and carbimazole can provide a “preview” of how the cat will be after curing hyperhthyroidism. Thus, some veterinarians attempt trial therapy with methimazole or carbimazole to test what renal function might remain after treating the hyperthyroidism. Except for advanced kidney disease, the necessity of this approach is questionable, given that treatment for the hyperthyroidism would still recommended in most cats. In support of that reasoning, the survival of cats that develop obvious kidney disease is not shorter than those that do not develop kidney disease after treatment of hyperthyroidism.

We will review your cat’s kidney tests and urinalysis prior to admitting your cat to Hypurrcat. If we find any signs of CKD, we will begin prophylactic measures to control the kidney disease while your cat is being treated. Even in cats with healthy kidneys, we always repeat kidney tests at the end of the treatment to ensure that kidney function has not deteriorated.

Again, if kidney disease does develop, it is not caused by the radioiodine. It was present before the treatment, but was masked by the hyperthyroidism.

Hyperthyroidism and Kidney Function: A Love/Hate Relationship Click here to watch the video

If your cat eats a particular kind of food, we suggest that you bring enough food for 7-10 days, as we want to maintain your cat's regular diet. We encourage you to bring one or more small personal items (e.g., a sock or toy) to place in your cat's cage. However, don’t bring anything of sentimental value because we cannot return these personal items; they may become contaminated with radiation.

When your cat’s radioactivity level is below the legal limit, we will contact you to make an appointment for discharge. When you pick up your cat, we will explain in detail the radiation safety precautions that you should follow for two weeks. If you wish to review the Release Information for Owners of Cats Treated with Radioiodine, you may find it at that link.

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 the following safety precautions for two weeks after discharge:
• You may cuddle with your cat for 20 minutes per day. You can have these twenty minutes all at once, or spread out throughout the day.
• Fortunately, you can pet your cat at an arm’s-length distance as much as you want; this is a safe distance.
• Your cat may not be on your bed while you sleep.
• Your cat should not be near children or pregnant women.

If you or a family member is pregnant, you cannot prevent contact between your cat and children, or you cannot keep your cat from sleeping on the bed with you at night, we recommend that your cat either remain at Hypurrcat or be boarded with your veterinarian during these two weeks.

Release Information for You and Your Hyperthyroid Cat After Treatment with Radioiodine Click here to watch the video

Your cat will excrete much of the residual radioactivity through urine and feces. Therefore, during the first 2 weeks after your cat has been discharged from Hypurrcat, you should either flush the soiled litter down the toilet or store it until it is no longer radioactive. During this initial 2-week period, you must never put waste collected in the regular trash!

To flush your cat’s litter, you must use a flushable litter. Although there are many brands of flushable litter, we use the "World's Best Cat Litter" at Hypurrcat, so your cat will be accustomed to that brand. You can purchase the World's Best litter at many local pet stores.

You should scoop the litter box at least once or twice a day. You should wear disposable latex gloves when changing the litter and wash your hands after you flush it. Once the 2-week period is over, you should wash the litter pan and litter scoop with soapy water and flush this wash water down the toilet. It is not necessary to discard these items.

If you do not wish flush the soiled litter down the toilet, the radioactive cat litter can be stored for a 3-month period to allow it decay down completely to nonradioactive levels. To store the litter, you should collect all the soiled litter for the first 2 weeks after treatment and place it into a heavy garbage bag, tying it securely. To help prevent odors, it is best to double bag the soiled litter. Place the double-bagged soiled litter in a large trash container with a tightly sealed, locked lid. During the time you store the container, place it in an area where it cannot be reached by small children, pets, wild animals, etc. (e.g., a basement, garage, or yard). Do not place it in your kitchen, bedroom, or other frequently occupied areas. After storing this litter for a 3-month period, the bagged cat litter can be disposed of as regular trash because it will no longer be radioactive.

The amount of radiation remaining in your cat is extremely low. The amount of radiation you might receive from your cat would be roughly equivalent to that received when you fly round-trip across the country. In fact, human patients can receive up to 10 times the dose of radioiodine and still go home on the day they get treated. The major reason for this discrepancy between cats and people is that human patients always flush their waste down the toilet, removing any radioactive contamination from the home. In contrast, cats generally use a litter box, keeping the radiation in the home.

Your cat has already excreted the vast majority of the radioiodine in urine and feces while your cat was at Hypurrcat during the first 5 to 10 days after treatment. Therefore, while these discharge instructions may seem alarming, they are an extremely cautious and conservative approach. If you or any of your family were to receive radioiodine therapy, the restrictions after treatment would be much less severe. If you follow our instructions, you and your family will receive almost no exposure whatsoever.

The amount of radiation that your other pets will receive by contact with your cat or by using the litter box is negligible. If you have multiple cats sharing the same litter box, however, we do recommend that you clean the box at least 2 to 3 times a day to remove the contaminated litter clumps from the box. Based upon Federal, State, and City guidelines, you do not need to quarantine your cat from other pets.

If you know that you cannot follow the recommended safety precautions (e.g., if you are pregnant or cannot avoid prolonged close contact, flush the litter, etc.), we recommend that you board your cat with your regular veterinarian during this 2-week period. Their staff would follow the same radiation safety guidelines you would, including properly handling the cat litter and avoiding close, prolonged contact with your cat.

After we treat and discharge your cat, we will repeat the thyroid, kidney, and liver function tests to gauge both the success of the treatment and your cat’s general health. We will remain involved throughout your cat’s recovery and review all the information with your veterinarian. After you pick up your cat from Hypurrcat, we will send your veterinarian a letter summarizing your cat’s treatment and recommending monitoring strategies. Your veterinarian can also contact us if he or she has any further questions.

The vast majority of cats require minimal aftercare. In most cases, your veterinarian should check the thyroid function 3 months after radioiodine therapy, then once a year after that.

Your cat’s behavior may change within a few weeks, but some cats require as much as 2 to 3 months for all the clinical signs to disappear. As the metabolic rate returns to normal, body functions slow down. Your cat will become calmer. Along with a slower heartbeat and respiration, changes may include weight gain, better grooming, less vomiting, reduced appetite, fewer visits to the litter box, and more sleeping. Some cats gain one or more pounds in the first month, whereas other cats put lost weight back on more slowly.

Yes, although it is very uncommon (less than 5% of treated cats). These recurrences usually develop 3 years or more after the hyperthyroidism was first treated. Therefore, such relapses may stem from a new thyroid tumor, rather than the first tumor re-growing.

Our research studies have shown that a single dose of radioiodine will cure 95% to 98% of hyperthyroid cats. Those cats that are not completely cured after initial treatment will still improve clinically because most of these cats have some decrease in their circulating thyroid hormone concentration. If your cat is in the small minority that is not cured within 3 months after treatment, we generally recommend retreatment with radioiodine as the best treatment method. Virtually all cats that remain hyperthyroid after the first treatment are cured by the second treatment.

At Hypurrcat, we repeat your cat's thyroid profile and kidney/liver profile on the day of release. Depending on the results of these tests, we will recommend that you recheck with your regular veterinarian in 1 to 3 months to assure that your cat’s thyroid function normalizes.

In most hyperthyroid cats treated at Hypurrcat, the serum thyroid hormone concentrations will already be normal when you pick your cat up. In approximately 20% of cats, however, it takes 1 to 3 months for the serum thyroid hormone concentration to normalize after the radioiodine treatment. If hyperthyroidism persists after the 3-month period, retreatment with radioiodine should be considered.

Once your cat’s thyroid function has normalized, additional thyroid rechecks are recommended once a year in order to monitor your cat's thyroid function.

The long-term prognosis for hyperthyroid cats treated with radioiodine is excellent. Many owners are hesitant to treat older cats with radioiodine. But remember, old age is not a disease. Almost all cats (including cats of all ages) return to normal health and live a completely normal life after radioiodine therapy.