WHAT IS HYPERTHYROIDISM?
Hyperthyroidism is a common problem in cats caused by excess production of thyroid hormone. In most cases it is caused by a benign tumor-like growth of the thyroid gland.

WHAT ARE THE SIGNS OF HYPERTHYROIDISM?
Excessive thyroid hormone levels can cause a variety of signs including weight loss, increased appetite, increased thirst, vomiting, diarrhea, rapid or labored breathing, hyperactivity and aggression. The most serious consequence is hypertrophic cardiomyopathy (thickening of the heart muscle) which can result in death. Heart changes are usually reversible, however, when thyroid levels are returned to normal.

HOW IS HYPERTHYROIDISM TREATED?
Hyperthyroidism can be treated in three ways. Each treatment has advantages and disadvantages.

• Surgical removal of the thyroid glands can cure the benign form of the disease but requires anesthesia and risks damage to nerves and nearby calcium regulating parathyroid glands.
• Methimazole is relatively inexpensive but must be given twice a day for life. This is available in tablet form or as a transdermal gel which is applied topically to the inner surface of the ear. Periodic follow-up testing is required to maintain proper regulation.
• Radioactive iodine treatment will cure 97% of hyperthyroid patients and rarely has side effects, but state laws require that treated cats be hospitalized in quarantine (approximately one week) until their radioactivity decreases to regulation levels. Radioactive iodine is considered to be the safest and most effective treatment for hyperthyroidism.

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