Radioactive Iodine Therapy for Hyperthyroidism

Hyperthyroidism is the most common endocrine disorder affecting mostly middle-aged and older cats. The large majority of cases are caused by a benign growth of the thyroid gland that produces excess levels of thyroid hormone (called thyroxine or T4).

The most common clinical signs seen in hyperthyroid cats include:
• weight loss
• changes in appetite
• changes in behavior [including vocalization, irritability, anxiety or nervousness]
• overall increase in activity level
• gastrointestinal signs including vomiting or diarrhea
• increased drinking and urination
• changes in the hair coat
• changes in cardiac function including high blood pressure, heart murmurs and arrhythmias

Untreated, hyperthyroidism can lead to marked weight loss and serious complications due to damage to a cat’s heart, kidneys, digestive tract, and many other organs.

Your Experience at Cats Only

Cats Only Vet Clinic is a certified Gold-status Cat Friendly Practice ® . This designation means that our practice has taken specific extra steps to ensure your cat will be provided with reduced stress during their stay and the highest quality level of care possible. Not only is the I-131 hospitalization area a feline-friendly environment having met specific standards for the facility and care of your cat while staying with us, but the nursing staff and doctors have been trained to approach and handle cats in a gentle, empathetic, and caring manner. During your cat’s stay following the radiation treatment, they will be moved to a radiation isolation ward and will be provided with environmental enrichment including calming classical music, a TV with fun nature videos and other cat-inspired flicks, and adequate space for sleeping, dining, and bathing. They will be offered three meals a day, with frequent litter box changes to minimize contamination.

During your cat’s stay, you will not be able to visit your pet. We will monitor their radiation levels daily and will discharge them from the hospital once their radiation levels have been documented below 1 mR/hr at the skin surface (usually three to five days after I-131 administration).

Is my cat eligible for I-131?

If your cat has been diagnosed with hyperthyroidism by your veterinarian, a referral form for I-131 treatment can be found here [hyperlink]. All hyperthyroid cats must first perform a methimazole challenge, before eligibility can be assessed. This requires your cat to be controlled medically with methimazole while showing stable kidney function at the same time.

Required laboratory tests include a complete blood count (CBC), comprehensive biochemistry profile with electrolytes, total T4, and urinalysis. Laboratory studies may be performed up to four weeks prior
to admission for I-131 treatment. Cats Only Veterinary Clinic may require additional testing if we feel they are needed for your cat’s safety.
Only clinically stable cats are accepted for treatment. If your cat is ill or has uncontrolled concurrent illness, they will need to be treated medically until they are deemed stable.

What to expect when your cat comes home

Because your cat will not be discharged until their radiation levels are low, an extremely low risk of radiation exposure will be present (similar to radiation exposure from one single chest x-ray) as long as safety precautions are met.

The following safety guidelines must be followed for 3 weeks following release:

• No exposure to infants, pregnant women, nursing mothers

• Close contact to your cat must be limited for 3 weeks following release. It is ok to be in the same room as them, but avoid snuggling and sleeping with them. Children
should avoid contact completely (stay at least 6 feet away from the cat) for 3 weeks
following release.

• Small amounts of radioactivity will be excreted in the urine and feces during the 3 weeks following discharge and special care is required for handing excrements. Rubber gloves must be worn while cleaning the litter box, waste must be sealed in a plastic bag and stored for 30 days from the date of injection. The waste bag may be stored in a garbage can and kept in the garage, basement, or outside. At 30 days post-injection, the cat is no longer radioactive. Return to normal litter box cleaning routine. The saved litter from the first 30 days, must be saved for an additional 60 days than can be disposed of at Day 90 with the regular trash. Pregnant women/nursing mothers should NOT handle litter during the first 90 days. Soiled gloves should go in the trash with the saved litter.

• Hands should be washed thoroughly after handling your cat or cleaning the litter

• Although not recommended for 30 days following injection, if your cat must travel
on an airplane following discharge, you will need a letter from your veterinarian
describing the treatment given.

• If litter gets on my skin or is spilled on the floor and/or my cat misses the box (house soils): wash hands with soap and water two or three times. Clean the soiled area on the floor two or three times. Soiled blankets can be washed in the normal laundry.

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