Radioactive Iodine Therapy for Hyperthyroid Cats

Portland Veterinary Emergency and Specialty Care is proud to offer radioactive iodine therapy for hyperthyroid cats. Dr. Gail Mason is leading our team in these treatments.

Radioactive I-131 is a highly effective and well-tolerated treatment for hyperthyroidism, a common medical condition affecting older cats that results in excessive thyroid hormone.

In most cases, the condition results from a benign tumor of the thyroid gland, which causes excess thyroid hormone secretion.

Excessive hormone secretion causes accelerations of bodily processes and clinical signs that are apparent to owners. Such signs include increased appetite, weight loss, rapid heart rate, muscle weakness, restlessness, vocalization, vomiting, diarrhea, increased thirst/urination, and heat intolerance.

Over time, the accelerated metabolism leads to deleterious effects on the cat’s internal organs. Resultant heart disease, kidney disease, and/or intestinal disease can ultimately lead to death. Fortunately, the disease is very familiar to veterinarians and is most often easily and rapidly diagnosed by measuring the level of thyroid hormone (T4) in the bloodstream.

The ideal goal of 1-131 therapy is to restore normal thyroid function with a single dose of radiation without permanently damaging normal thyroid tissue. Most hyperthyroid cats treated with 1-131 are cured by a single injection — No surgery! No anesthesia! No medication!

Successful treatment results in normal thyroid hormone levels within 2 weeks of treatment in 70-8O% of cats. Over 90% of treated cats reach normal hormone levels within 3 months post-treatment. Cats often feel better within days of treatment and most owners can expect gradual and steady health recovery within 2 months. If you think radioactive iodine therapy for hyperthyroid cats could be a help to your pet, please talk to your family veterinarian about a referral.

Pre-Treatment Diagnostics

These diagnostic tests are required before your cat can be admitted for radioactive iodine therapy. We recommend that these tests be completed at your regular veterinarian’s office one to two weeks before your radioactive iodine consultation. If these tests have not been completed, they can be completed at the time of your radioactive iodine therapy consultation.

All cats must have up-to-date vaccinations before being brought in for treatment.

Lab Work

  • CBC, Chemistry
  • SDMA
  • Urinalysis
  • Thyroid level

 

Whole-Body Radiograph

  • Radiograph(s) can be emailed to PVESC if digital, or brought with you to your appointment

Medical Follow-Up

Copies of all pertinent medical records and test results regarding your cat’s treatment will be forwarded to your primary care veterinarian. We recommend a recheck examination, thyroid (T4) level, and kidney (renal) profile with your veterinarian 2-3 months after I-131 treatment. Please have the results forwarded to PVESC.

Discharge Instructions

FOR OWNERS OF RADIOTHERAPY-TREATED CATS

Download Instructions Here (PDF)

For the first two weeks please follow these detailed home instructions for handling your cat and litter waste.

Please note that if you cannot or will not follow these instructions, you must notify us, and we may need to keep your cat hospitalized for additional time before release (additional fees apply).

The thyroid hormone level continues to decline for 30 to 60 days after treatment. During this time, the symptoms of hyperthyroidism are expected to abate. Gradual weight gain and return to healthy body condition are expected. If your cat is showing signs of illness or depression, please contact PVESC.

Upon discharge from PVESC (after an average of 4 to 7 days after treatment), treated cats will still be excreting radioiodine in their urine, saliva, and feces. This radioiodine is in a form that can be taken up by the human thyroid where it may cause damage. Even though the level of radioactivity is much lower than the level at which human patients are released from the hospital, you must exercise caution during this period. The remaining radioactivity will be gradually eliminated from the cat over the next average of 3 to 6 days.

  1. Treated cats must remain indoors only for two weeks after discharge.
  2. Pregnant women, children under eighteen, and people with immune-mediated diseases should not have any contact with the cat or litter pan for two weeks.
  3. Prolonged close contact with your cat (under 3 to 6 feet) must be avoided during this time. Limit visits to 20 minutes per session. Visit and pet your cat briefly, but do not allow the cat to sleep on your bed with you. Avoid contact with urine and saliva and do not allow the cat to sleep on your bedding.
  4. Foods containing fish products can be reinstituted post-treatment.
  5. Use disposable litter pan liners and plastic gloves to minimize handling of litter/waste.
  6. Wash your hands after handling your cat, its food dishes, and litter pan.
  7. There is no need to quarantine your cat from other pets in the household.
  8. If your cat must be seen by a veterinarian before the end of the 2-week quarantine, please alert PVESC staff.

While the amount of radioactive material remaining in your cat’s body is low, it is prudent to follow the above instructions exactly. If this is not possible, please consider boarding your cat with PVESC during the quarantine period (additional fees apply).

WASTE DISPOSAL

Disposal of litter pan contents:

If your home is on a public sewer system:

  1. Use scoopable/flushable litter such a “World’s Best Cat Litter” or Swheat”
  2. Wear protective gloves (such as dishwashing gloves), scoop your litter pan twice per day, and flush the waste down the toilet.
  3. At the end of the two-week quarantine, flush all remaining litter down the toilet. The litter pan and scoop can be washed with soapy water. Flush the used soapy water down the toilet; it’s not necessary to save these items for any extended period or to discard them.
  4. This is the approved method of the State of Maine Nuclear Regulatory Commission.

If your home has a private septic system or if you have a public sewer and choose not to flush it:

  1. Your cat’s litter box must be scooped twice per day.
  2. Wear protective gloves (such as dishwashing gloves) and place the waste in a Ziploc or tie bag, be sure to double-bag the litter and excretions, then place the bag in a plastic tote with a locking lid that has been lined with a large garbage bag. This tote should be stored outside and away from small children, other pets, and wild animals.
  3. At the end of the two-week quarantine, add all of the remaining litter from the boxes to the trash bag in the outside tote, tie the bag and leave all waste until the 80-day mark on your calendar.
  4. The litter pan and scoop can be stored with the trash bag in the tote for 80 days. It can then either be thrown out or washed and reused.
  5. When it is time to discard the waste, simply remove the large garbage bag from the tote and dispose of it as you would your household trash. The tote itself may be disposed of separately or can be rinsed out and reused.
FOLLOW UP

We would like to recheck your cat’s progress in 4 to 6 weeks. This includes a physical examination, thyroid level (T4), renal panel with SDMA, electrolytes, and body weight. If you prefer to see your primary care veterinarian for this, please have the results forwarded to PVESC.

Meet Our Radioactive Iodine Therapy for Hyperthyroid Cats Doctors

Gail Mason

Gail Mason

DVM, MA, DACVIM, Oncology, Internal Medicine
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