Rebound hypothyroidism in a cat

Re: Rebound hypothyroidism in a cat

Kirsten Simpson — Sun, 12 Jul 2009 23:25:14 GMT

Aww thats a shame to hear :( Sounds like there was something more sinister going on rather than her low T4 levels? Sounds like something neurological, poss tumour or something in the brain?

Re: Rebound hypothyroidism in a cat

Hanna Bennett — Sun, 12 Jul 2009 12:34:53 GMT

Well, cat is no longer with us so thanks for the thoughts anyway. Became more and more obtunded throughout the day yesterday, and developed blown pupils with no PLR or menace, ataxic and tremors. Discussed referral but felt px was poor whatever the dx and cat deteriorating at such a rate it seemed unfair to delay the inevitable.

Re: Rebound hypothyroidism in a cat

Hannah Wynne Richards — Sat, 11 Jul 2009 09:35:59 GMT

Refer if owner will pay for it, otherwise continue symptomatic treatment. HR suggests it's working but a delayed response. Sorry, no other bright ideas

Wynne

Re: Rebound hypothyroidism in a cat

Hanna Bennett — Sat, 11 Jul 2009 08:47:36 GMT

Am trying to get a urine sample - planning to keep the cat in today to drip her anyway so will acheive that hopefully in the meantime. Heart rate has dropped from 200+ to 180 to 140 at last visit which certainly backs up the low thyroid level, no dyspnoea even when stressed. Was thinking u/s abdo +/- chest rads anyway to try and rule out other possiblities. Having said that we've had a few cats do this and most of them recover once you stop the medication, this one is just not responding as well as they usually do.

Re: Rebound hypothyroidism in a cat

Laurence Webb — Fri, 10 Jul 2009 22:40:28 GMT

My first thought is that this is not simply a problem of hypothyroidism and that the low TT4 is due to non-thyroidal illness.

As far as I am aware methimazole simply prevents thyroglobulin conversion to T3 and T4 but has no effect on the thyroid itself - certainly I've never appreciated a reduction in the size of the thyroids following treatment. - and withdrawing the drug normally results in a rebound of the TT4 to pre-treatment levels within a couple of days as overprodution of thyroglobulin is still continuing.

Is the cat quite thin - if so then creatinine levels may well be within the normal ranges so CRF shouldn't be discounted so I'd check USG +/- UPC if the sediment is inactive. http://www.iris-kidney.com/ has some useful guidelines to look at and you'll note that, in the face of low USG, the 'normal' lab ranges for creatinine are irrelevant.

Failing that I'd go on a fishing trip to rule out any other non-thyroid related problems. Have you looked at bile acids as well as just the liver enzyme levels and checked you haven't got a thyroid related complcation such as a pleural effusion or thrombus developing.