Treating Feline Hyperthyroidism

Hi, Dr. Neely,

If you had a 15 yr. old cat who was diagnosed as hyperthyroid (t4 - 5.5), but also had bilirubin in the urine, how would you treat?

There are warnings against giving Methimazole with liver disease - do vets heed this warning in the real world?



Hi, Cathy,

I have rarely, if ever, seen a hyperthyroid cat that did not have elevated liver enzymes at the time of diagnosis. That is a common abnormality associated with untreated hyperthyroidism. We always go ahead and treat these cats with Methimazole initially and then either continue Methimazole, surgically remove the thyroid glands, or send them for radioactive iodine treatment.

However, bilirubin is NOT one of the substances that we generally find elevated. Therefore, I would recommend that the liver be further evaluated before starting the Methimazole. I have seen a few cats that have had a problem with liver disease after starting Methimazole and the reaction can be quite severe. Therefore, I personally take the warning about Methimzaole and prior liver disease seriously.

The results of further liver diagnostics may reveal that Methimazole will be safe. If not, there are surgical options and radioactive iodine treatment available. The one thing you don't want to do is NOT treat the hyperthyroidism at all. Left untreated, your kitty's heart will be destroyed.

Thank you for your question,
Dr. Neely


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