Hyperthyroidism is the most common endocrine disorder in cats older than 8 to 10 years of age. This disorder is generally caused by a non-cancerous growth of the thyroid gland. Clinical signs of hyperthyroidism are weight loss, increased eating and/or drinking, vomiting, diarrhea, rapid heart rate, heart murmurs or irregular beats, irritability, and possibly a mass in the throat area.
Diagnosis of hyperthyroidism is confirmed by an elevated serum thyroxin (T4) level or abnormal thyroxin level when tested by equilibrium dialysis. Occasionally further testing may be needed to help confirm the diagnosis. These tests are easy to run and all that is needed is a small amount of blood.
Treatment consists of three possible options:
- Tapazole is an oral medication given two to three times a day for the life of the cat. This drug blocks the thyroid hormone synthesis in the gland. There can be side effects which can improve over time. This drug can also have some bone marrow side effects and frequent blood tests are needed for the first few months after starting the medication.
- Surgical removal of the thyroid glands is another option. The cat is prepared for surgery with medication to lower the levels of thyroid hormone. Excessive thyroid hormone can have temporary effects on the heart. Additional tests such as chest radiographs and ECG are needed to completely evaluate the heart prior to surgery.
- Radioactive iodide therapy is available locally and is easy to administer. This is a radioactive isotope of iodide which concentrates in the thyroid tumor cells and destroys them. This is 90-95% effective and no further treatment is needed. There is no life-long need for medications and the risk of surgery is eliminated.
Hyperthyroidism is a very treatable disease and its effects on the body and its functions can be greatly minimized or eliminated if caught early. A yearly blood screen, which includes a thyroid screen, is recommended on all cats seven years of age or older. Please do not hesitate to ask us about this very treatable disease.