Your Cat Has Hyperthyroidism

by | May 17, 2021

Your Cat Has Hyperthyroidism


What is hyperthyroidism?

Hyperthyroidism is a condition of an excess of thyroid hormone in the body. It is most commonly caused by a benign tumor (adenoma) in the thyroid gland; or less commonly, a malignant tumor (adenocarcinoma).
Is it serious? Yes, because it causes an uncomfortable rise in the metabolic rate of the body (think 5 cups of coffee!) which leads to the over functioning of all organs and tissues in the body. Hyperthyroidism can cause other diseases, such as high blood pressure, or can mask other diseases, such as kidney disease. Going untreated will eventually cause organ failure.

Can it be treated?

Yes, it is a very treatable condition. There are four ways to treat Hyperthyroidism:

  1. Surgery – A surgery can be performed to remove the tumor in the thyroid gland and usually involves a two-day stay at the hospital and only one wing of the thyroid is removed at a time. Due to the parathyroid glands this surgery can cause hypocalcaemia and your cat may require thyroid medication post-surgery.
  2. Radioactive Iodine (I 131) – This is a procedure that uses a single injection of radioactive iodine under the cat’s skin which targets and destroys the tumor in the thyroid gland. This procedure is carried out in the Vancouver area, it needs no anesthetic, and it usually requires a 10-day hospital stay so that the radioactive levels are low enough for the patient to go home safely.
  3. Medication – Methimazole is a medication that lowers the excess thyroid hormone and comes in many forms. After starting a new dose, it is necessary to repeat the thyroid test in 30 days. After control is established, a blood panel and blood pressure test should be done one month later, to screen for conditions that may have been “hidden” by the hyperthyroidism.
  4. Diet – There is a restrictive diet food which deprives the body of iodine with a subsequent lowering of thyroid hormone. Cats do not always find this food palatable and can have NO other foods or treats.

How do we start therapy?

Once a cat is diagnosed, we begin treatment with Methimazole. This medication blocks the formation of thyroid hormone and thus lowers its level in the blood, resulting in a lower metabolic rate. The medication is given twice a day for 4 weeks; then a recheck for follow-up blood/urine tests and blood pressure, to ensure they are on the proper dose.

When my cat is stabilized, what do we do?

We continue with the chosen treatment, but thyroid values may fluctuate over the life time of your cat, so thyroid testing is required every 6 months.

What is the prognosis for a hyperthyroid cat?

Once controlled the quality of life is similar to that of a healthy cat, but medication is required lifelong. Recent research has revealed that after four years of medical treatment, the benign adenoma can become malignant. Consequently, it is advised to have either thyroid surgery or Radioactive Iodine treatment within 4 years of the initial diagnosis. Once stabilized, your cat remains on Methimazole and requires semi-annual visits which may include a blood screen, urinalysis and blood pressure.

Case Study

Meowington, a 15-year-old male, came in for an illness exam for rapid weight loss despite having a good appetite and energy. Our doctor recommended a senior blood screen to access organ values, proteins, and blood cells. Since we have in-house lab work, we are able to run blood and have results within 30 minutes. His T4(thyroxine) value was over 8.0 where a normal T4 would be within 2.0-4.0! The test came back positive for hyperthyroidism. This explains his rapid weight loss but ravenous appetite, among other abnormalities.
There are many ways to treat hyperthyroidism, but Meowington’s owners chose to treat with thyroid pills. Meowington’s owners were instructed to return for another thyroid blood test in 1 month. This recheck is incredibly important as it allows the doctor to prescribe an accurate dose to treat this disease. Unfortunately, Meowington’s owners did not bring him back until 4 months later for new problems. We tested his thyroid again and it was severely uncontrolled and had lost more weight, it was not looking good!
Meowington was re-prescribed thyroid medication and his owners brought him back every month for 3 months until his thyroid levels were controlled. He had gained back his healthy weight! Since he is doing so well now that his thyroid is controlled, he does not have to visit the hospital again for another 8 months and continues to take his medication like a champ!
If you think your cat may be suffering from this condition, we invite you to call us for an appointment.
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