Over the years we have treated a large number of hyperthyroid cats. As these cats go on to live long, healthy lives, we have started to see a small number of cats (1-2%) that re-develop a hyperthyroid state. In these cats, the average time of recurrence is 3 or more years after first treatment. We retreated one kitty that re-developed hyperthyroidism 10 years after treatment when he was 17!

The recurrence of hyperthyroidism is not from failure of the first treatment; if this were the case, the cat’s thyroid levels would not normalize after treatment. Rather it is due to the cats growing a new tumour in their thyroid gland. Tumour cells are transformed from normal thyroid cells and since RAI spares normal thyroid cells, it makes sense that a growth of a new tumour could occur in the future.

Fortunately for the cats and their owners many of these cats are good candidates for a second RAI treatment. There is no reason they can’t be cured again with RAI and there are no adverse effects on their health by having a second treatment. The owners of cats who redevelop hyperthyroidism readily retreat their kitties with RAI. They tell us they are grateful for the past years where they did not have to give their cat pills, that their cat was happy and healthy in this interval, that they know it was a cost effective decision and they are eager to have their cat cured a second time.