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Hyperthyroidism is the clinical syndrome that exists when there is overproduction of circulating thyroid hormone, which is the hormone that regulates the body’s metabolism.  Hyperthyroid cats have a high metabolism that affects multiple organ systems.  Radioactive iodine (I-131) therapy is a non-invasive, highly effective therapy for feline hyperthyroidism.

Hyperthyroidism is a disease commonly seen in middle to older aged cats. The cause of this condition is most often due to benign, yet abnormal growth of functional thyroid cells, which are secreting the thyroid hormone.  Some of the most common signs of hyperthyroidism are increased appetite, weight loss, increased heart rate, anxiety, increased vocalization, and increased water intake and urination.  If untreated, the increased levels of thyroid hormone caused by this disease can affect multiple organ systems, and can cause changes to the cardiac muscle.  The excess thyroid hormone also increases the blood flow to the kidneys, which can mask renal disease.

As part of our commitment to delivering the highest quality care, our I-131 patients are given a diagnostic scan prior to I-131 therapy. Diagnostic scanning helps to ensure that we are treating cats appropriately and successfully.  Our I-131 program is administered and directed by our board-certified radiologist.  Additionally, as part of our affiliation with City of Angels Veterinary Specialty Center, we provide on-site 24-hour care for our patients and access to the other specialty practices, if necessary. 

All of our I-131 patients are housed in cat condominiums.  The “cat condos” are one bedroom accommodations with a loft and a private bathroom.  The condominiums are contained in a well-lit room with natural sunlight and a view of palm trees.  Relaxing music complements the atmosphere, with each patient receiving a daily medical evaluation by a veterinarian and frequent visits by our SCVI staff. 


Prior to treating a patient with I-131 therapy, Southern California Veterinary Imaging performs a simple and non-invasive diagnostic scan with Tc-99, allowing us to visualize the size, shape, and margination of the thyroid gland (left and right lobes).

This diagnostic scan also assists in determining if disease is unilateral or bilateral. A recent study in the Journal of the American Veterinary Medical Association found that cats with bilateral disease are two times more likely to become hypothyroid than cats with unilateral disease. 

While the majority of hyperthyroid cats have benign disease, this diagnostic scan allows us to rule out more aggressive diseases such as carcinoma, which has a 1-5% reported incidence in cats. A diagnostic thyroid scan also helps us determine if ectopic thyroid is present elsewhere in the thorax.

This diagnostic scan also helps provide us with as much information as possible for our owners prior to treatment. At Southern California Veterinary Imaging we use this information, along with the T4 levels, to determine the appropriate dose of  I-131 for each patient.

The diagnostic scans for I-131 therapy are usually performed on a Monday. After evaluating the results, our cats receive their subcutaneous injection of  I-131 on Tuesday.  Patients are monitored over the next few days while they relax in our spacious one bedroom cat condominiums with a loft, private bathroom, and plenty of sunlight shining through our large windows. Most patients are ready to go home by Friday.

There are specific guidelines our patients must follow for the first two weeks at home after treatment.  If it is not possible for the guidelines to be followed at home, our patients are welcome to stay with us a bit longer. 

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