Radioactive iodine

Re: Radioactive iodine

Rob Loxley — Wed, 27 Aug 2014 08:49:06 GMT

[quote user="Stephen Courtney"]the dose of radioactive iodine required to treat malignant thyroid tumours is far, far higher than those required to treat normal hyperthyroidism in cats - I'm not sure anyone does it[/quote]

AFAIK, only Bristol

Re: Radioactive iodine

Virginia Campbell — Wed, 27 Aug 2014 01:09:35 GMT

[quote user="Nicola Lawlor"]The radioactive iodine is taken up by the overactive cells and this is what destroys them, therefore they need to be off meds for best effect - meds block the conversion of iodine into thyroid hormone.[/quote]

Makes sense...but Vidalta and the rest stop working fairly quickly, right? As in, could you give the last dose a few days beforehand and still have good iodine uptake and processing when the I131 was given? Or could "pretreat" with y/d then swap to Whiskas and milk on the day :-)

They taught us in college (15 years ago) not to leave a hypert4 cat uncontrolled to "treat" renal failure-we were taught to go ahead and make the cat euthyroid then control the kidneys as best we could- so this idea has been around a good while. I used to think that the insistence on pretreatment before I131 was:

- for the noble aim of making the heart stable and safer in the unfamiliar and therefore stressful environment of the hospital and under sedation

- for the noble aim of unmasking and identifying the few really bad CRFs that are going to crash and burn to stop the owner spending ££££ only for it to be euthed a few weeks later

- for the slightly less noble aim of reducing the risk of having cats nosedive into clinical CRF on their watch rather than the GP vet's watch (at least now with shorter post-treatment quarantine times such cats are more likely to make it back home before they decline so the GP vet gets to have that bad-news conversation)

- possibly also for the less noble aim of excluding any cats with dodgy kidneys to keep their post treatment survival time statistics shiny.

Happy to be corrected on any point.

Re: Radioactive iodine

Stephen Courtney — Wed, 27 Aug 2014 00:27:35 GMT

I have never seen a malignant thyroid tumour in a cat, let alone a functional one. I doubt an FNA would be reliable enough to characterise such tumour with certainty - so you would be looking at a biopsy to be sure.

the dose of radioactive iodine required to treat malignant thyroid tumours is far, far higher than those required to treat normal hyperthyroidism in cats - I'm not sure anyone does it, or what the quarantining implications are, but i seem to recall that the prognosis is pretty poor regardless. Open to correction though!

Regarding normal referrals for radioactive iodine, there is usually a waiting list - 2 months the last time I checked - so you would need some sort of treatment initially, and i think this would be justified in case treating the thyroid unmasked renal issues - you can always fiddle a dose of meds but you can't undo surgery or radiation treatment.

Re: Radioactive iodine

Andrew Kent — Tue, 26 Aug 2014 21:47:59 GMT

It depends on the centre, many still want pre-treatment medical management but, based on the work suggesting that development of azotaemia during treatment doesn't worsen prognosis, some centres have therefore decided not to insist on pre-treatment. Whether this is a good idea or not is up for debate!

I don't think cytology would be sufficient to diagnose malignancy so I wouldn't advise it.

Re: Radioactive iodine

Nicola Lawlor — Tue, 26 Aug 2014 21:43:46 GMT

The radioactive iodine is taken up by the overactive cells and this is what destroys them, therefore they need to be off meds for best effect - meds block the conversion of iodine into thyroid hormone.

No idea on the malignancy question though sorry.