Radioactive Iodine (I131)

Feline Hyperthyroidism

Hyperthyroidism is a common disorder of cats that occurs when the cat's thyroid gland produces an excess of thyroid hormone. An excess of thyroid hormone affects all of the cat's organ systems.
 
Hyperthyroidism occurs in middle aged and older cats. Both feline sexes and all breeds are equally at risk.
 
The thyroid gland in cats has two separate lobes and is located in the neck region. Hyperthyroidism is caused by a tumor in this gland. Ninety-eight percent of these tumors are benign (adenoma) and two percent are cancerous (carcinoma). Seventy percent of cats have both thyroid lobes affected by tumor.
 
Symptoms of Feline Hyperthyroidism may include:
 
  • Weight loss
  • Changes in behavior - anxiety or nervousness
  • Excessive appetite or decreased appetite
  • Increased water intake
  • Hyperactivity or lethargy
  • Excessive shedding, hair loss (alopecia), poor coat condition
  • Diarrhea or vomiting
  • Increased urination
  • Cardiac symptoms - rapid heart rate, arrythmia
 
Feline Hyperthyroidism is fatal if left untreated, but the cat can live a normal life with proper treatment.
 

Treatment of Feline Hyperthyroidism

Treatment with radioactive iodine (radioiodine; I-131) is the preferred treatment for cats with hyperthyroidism (and well as in humans). It is as easy as one injection just under the skin, much like a routine feline vaccine. Radioiodine is safe and effective.
 
The I-131 is absorbed quickly into the cat's bloodstream and the diseased thyroid tissue. Once in the thyroid, it destroys the overactive portions of the thyroid gland. The radiation is excreted primarily through the urine with a lesser amount in the stool. Law requires a short stay (five to ten days) at The AMC facility until the cat's level of radiation has fallen to an acceptable level.
 
The radioiodine treatment has advantages over medical and surgical treatments for feline hyperthyroidism.
 
  • No anesthesia is required
  • No daily medication
  • Does not destroy healthy tissue
  • Does not damage other tissue or organs, including
    the parathyroid glands
  • Does not have harmful side effects
  • Returns thyroid function to normal usually within one month
  • Is cost effective
 
At The Animal Medical Center, the radioiodine procedure is performed by Dr. Mark E. Peterson, who discovered hyperthyroidism in cats and first devised the radioiodine treatment as a means of treating this common feline condition in 1980. Dr. Peterson is a world-renowned authority on feline hyperthyroidism and has 25 years of experience treating cats with radioiodine.
 

Contact Us

If you wish to contact Dr. Peterson's office directly to obtain additional information or to make an appointment, call our Radioactive Iodine Coordinator, Christina DeMarco at (212) 329-8658.
 
Alternatively, you can email Ms. DeMarco at Christina.demarco@amcny.org or fax us at (212) 486-1699.