Feline Hyperthyroidism

Treatment with radioactive Iodine-131 is the gold standard of treatment for hyperthyroidism in humans and feline patients.  A technetium scan is a diagnostic test commonly.

Hyperthyroidism is a condition of abnormally elevated thyroid hormone levels usually caused by a benign thyroid adenoma.  This disease commonly affects our older cats and can cause weight loss despite a voracious appetite, hypertension, change in voice, poor hair coat and hyperactivity.
Radioiodine treatment is the treatment of choice for this condition because the only tissue in the body that uptakes iodine is thyroid tissue that is actively making thyroid hormone. This means the only tissue to take up radioactive iodine in a hyperthyroid cat is the thyroid tumor.

Technetium -99 is a shorter acting radioactive isotope that behaves like the Iodine -131 in that it is taken up by the abnormal thyroid tissue. This allows us to take an image of the location and size of the abnormal thyroid tissue with a special gamma camera. However, Tc-99 has a half-life of only 6 hours.  This allows it to be cleared quickly without affecting normal patients that do not need radiation treatment.

We utilize the image created by the Tc-99 scan to confirm the hyperthyroid diagnosis.  We also determine the amount of I-131 that each patient should be treated with based on the amount of disease visualized.  This allows us to decrease the dose the average cat is treated with and subsequently fewer of our patients require thyroid.

A normal patient ‘s Tc-99


Hyperthyroid cat with a single nodule


Hyperthyroid cat with bilateral nodules


Hyperthyroid cat with metastatic disease consistent with a thyroid


This patient has disease inside of the chest that cannot be found without a Tc-99 scan



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