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Radioactive Iodine Therapy

(I-131)

Radioactive Iodine, I-131, is a safe and effective, minimally invasive option to treat cats with hyperthyroidism.  Following one subcutaneous injection of I-131, over 98% of affected cats are cured of the disease. If needed, a second injection can be given. There are no harmful side effects.

How Does It Work?

Iodine is normally taken up by the thyroid gland. One form of iodine, I-131, is radioactive. When I-131 enters the thyroid gland it destroys the abnormally functioning cells. This reduces the size of the gland and its ability to produce thyroid hormone.

Symptoms of hyperthyroidism
  • Weight Loss
  • Increased Appetite
  • Vomiting
  • Diarrhea
  • Hypertension
  • Polydipsia – Increased Thirst
  • Polyuria – Increased urination
  • Nervousness
  • Hyperactivity or lethargy
  • Behavioral changes
  • Cardiac Issues:
    • Tachycardia – rapid heartbeat
    • Heart Murmurs
    • Arrhythmias – irregular heartbeat
What Is Hyperthyroidism?
Hyperthyroidism is a clinical condition resulting from the excessive production of thyroid hormones by the thyroid gland. It is more commonly found in middle-age to older cats. In fact, more than 95% of cases occur in cats over 8 years of age. This is usually due to benign changes (hyperplasia or adenomas) in the thyroid gland. Cancer of the thyroid gland can occur in cats, however it is rare.
additional treatment options

Medical treatment consists of giving oral or topical medication two or three times daily for the remainder of the cat’s life. The medication does not cure the disease; it merely controls the release of thyroid hormone. There is an incidence of side effects such as vomiting, diarrhea, poor appetite, and skin lesions. Missed medication will result in relapses.

Surgical removal of the affected thyroid gland(s) will cure the disease. Potential anesthestic risks in older, frail cats may eliminate surgery as a viable option.

Does My Cat Have To Stay In The Hospital?

Yes. Cats treated with radioactive iodine must remain hospitalized for 4-7 days following the injection. This is when they are most radioactive. Their level of radioactivity is checked daily with a Geiger counter (see below). When it reaches an acceptably low level, as determined by the Nuclear Regulatory Commission (NRC), they can safely go home.

Department Doctors

I-131

Internal Medicine

I-131

Primary Care & Wellness, I-131

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