Radioactive Iodine (I-131) Treatment for Feline Hyperthyroidism

June 1, 2021

Radioactive Iodine (I-131) Treatment for Feline Hyperthyroidism

Hyperthyroidism is a common feline medical condition, affecting approximately 10% of cats 9 years of age or older. Several feline hyperthyroidism treatments are available, however, only I-131 therapy offers a lifetime cure with few side effects. Virginia Veterinary Centers are fortunate to have on staff Dr. Morgan Brown, one of our highly trained veterinarians who has a special interest in this invaluable treatment. If your family veterinarian has diagnosed hyperthyroidism in your cat, I-131 may be the answer to your concerns about surgery or a lifetime of daily medication. 

What is hyperthyroidism in cats?

Your cat’s thyroid gland, which is located in their neck, produces thyroid hormones that regulate many of the body’s metabolic activities. Hyperthyroidism develops when the thyroid gland produces excess thyroid hormones, which increases metabolism, and has far-reaching effects on many body functions. 

What are hyperthyroidism signs in cats?

Increased metabolism overstimulates your cat’s various organs, and causes a variety of signs, including:

  • Weight loss
  • Appetite changes
  • Activity changes (e.g., hyperactivity or lethargy)
  • Behavior changes
  • Hair loss
  • Increased water intake
  • Increased urination
  • Diarrhea
  • Vomiting
  • Increased heart rate

Over time, untreated hyperthyroidism can tax your cat’s various body systems, and effects can be fatal. 

How is hyperthyroidism diagnosed in cats?

Your family veterinarian can diagnose hyperthyroidism with a blood test that measures thyroid hormone levels, as well as other hormones that stimulate the thyroid gland. An increase in your cat’s thyroid hormone level indicates hyperthyroidism. Your veterinarian may perform additional tests to evaluate your cat’s overall health and determine whether they are a candidate for I-131 therapy, including:

  • Complete blood count
  • Blood chemistry
  • Urinalysis 
  • Testing for feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV)
  • Thoracic X-rays
  • Abdominal X-rays
  • Cardiac and abdominal ultrasound (ultrasounds are not always required but may be requested prior to treatment for certain cases after an initial consultation)

These tests are required prior to I-131 treatment and should be performed by your family veterinarian before your cat’s consultation. 

What treatment options exist for hyperthyroidism in cats?

If your cat has been diagnosed with hyperthyroidism, prompt treatment is required to normalize their thyroid hormone levels and prevent systemic side effects. The goal for feline hyperthyroidism treatment is to reduce thyroid hormone production, which can be accomplished by one of four methods:

  • I-131 treatment — I-131 is administered as a single injection that is absorbed by the thyroid gland and destroys excess thyroid tissue. I-131 offers a life-long cure for hyperthyroidism, without the need for anesthesia, surgery, or daily medication. Cats typically have normal thyroid hormone levels one to two weeks after treatment. 
  • Anti-thyroid medication therapy — Medication that decreases thyroid hormone production can be prescribed for your cat; however, medication is typically administered twice daily for the rest of your cat’s life, which poses many challenges, is often stressful for cats and owners, and can weaken the pet-owner bond. Medication is fairly inexpensive, and often seems a more economical option to pet owners, but the cumulative expense of life-long medication, along with frequent veterinary visits and blood tests to monitor thyroid hormone levels, adds up to a significant cost over a pet’s lifetime.
  • Thyroidectomy — Surgery to remove the thyroid gland offers a lifelong cure but requires anesthesia, which can be risky if your cat has heart disease, high blood pressure, kidney impairment, or other problems secondary to hyperthyroidism. A common thyroid surgery complication is accidental damage to the tiny parathyroid glands that help regulate body calcium levels. Since I-131 treatment is non-invasive, does not require anesthesia, and does not affect the parathyroid glands, surgery is rarely performed.
  • Iodine-restricted diet — Limiting dietary iodine may help regulate thyroid hormone production, as iodine is a key component of the hormones. This treatment method may not be as effective as other options but can be useful for cats who have medical conditions that make other treatment methods impossible. 

How do I know if I-131 is the best treatment option for my cat’s hyperthyroidism?

After a hyperthyroidism diagnosis by your family veterinarian, schedule an appointment at our Richmond location to see if your cat is a candidate for I-131 treatment. I-131 treatment is ideal for cats who are medically stable, with no clinically significant cardiopulmonary, gastrointestinal, kidney, liver, endocrine, or neurologic disease. Since treatment does not require anesthesia or surgery and is non-invasive, most cats with hyperthyroidism are good candidates. If your cat is not a candidate for I-131, we will discuss other treatment options, and possible stabilization, to prepare for future I-131 treatment.

What can I expect when my cat has I-131 treatment at VVC?

If your cat is scheduled for I-131 treatment with Dr. Brown, you will be given specific instructions prior to admission. Some things to keep in mind include:

  • Medication administration — Your cat must stop taking thyroid medication, and possibly other medications, at least seven days prior to I-131 administration. Let us know about all your cat’s medications, so we can inform you if they should be stopped.
  • Hospitalization period — I-131 therapy involves the use of radioactive iodine, which is unsafe for human exposure at high doses. After treatment, your cat will be hospitalized in our nuclear medicine ward for approximately three to five days, to prevent human exposure. According to federal radiation safety guidelines, you cannot visit your cat during this time, or remove them from our hospital early. 
  • Homecare precautions — After release from the hospital, your cat will emit low radiation levels for up to 12 weeks, so you will be instructed to minimize human exposure by limiting your cat’s interactions with people and other pets, properly disposing of waste, and avoiding contact with contaminated objects.

If your cat has been diagnosed with hyperthyroidism, contact us to find out if I-131 can offer them a lifelong cure.