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thomas.dometios@pb.com
November 1st 05, 01:08 PM
Has anyone had their cat swing hypothyroid after having the Radiocat
treatment? Our 10 year old cat had bloodwork 3 months after the
procedure and it showed that he is now hypothyroid. The Vet said this
happens sometimes but they usually don't treat it unless the symptoms
(excessive weight gain, lethargy, etc.) become really bad. He did go
from about 10.5 lbs in June to 11 lbs. 13oz. at the end of October. He
is sleeping a lot and doesn't really have much energy. I hope we don't
have to treat this since one of the reasons we had the procedure was to
eliminate the need to medicate him daily. Also, can the hypo. be
temporary/transient? Thanks.

Phil P.
November 1st 05, 05:05 PM
> wrote in message
ups.com...
> Has anyone had their cat swing hypothyroid after having the Radiocat
> treatment? Our 10 year old cat had bloodwork 3 months after the
> procedure and it showed that he is now hypothyroid. The Vet said this
> happens sometimes but they usually don't treat it unless the symptoms
> (excessive weight gain, lethargy, etc.) become really bad. He did go
> from about 10.5 lbs in June to 11 lbs. 13oz. at the end of October. He
> is sleeping a lot and doesn't really have much energy. I hope we don't
> have to treat this since one of the reasons we had the procedure was to
> eliminate the need to medicate him daily. Also, can the hypo. be
> temporary/transient? Thanks.

Yes it can - but it depends on the dose of I-131. If your cat received a
large dose, hypothy could take longer to resolve or it could become
permanent. Many
cats go through transient hypothyroidism after radioiodine tx. -- it
takes a little time for thyroid-stimulating hormone (TSH) secretion to kick
in again and for the atrophied thyroid tissue to become functional again.
Most cats don't require treatment unless they become symptomatic - which
isn't common.

Many radio facilities routinely administer high doses of I-131 to guarantee
the destruction all the hyperfunctioning thyroid tissue in one shot. The
high doses certainly accomplish that, all right, but they also greatly
increase the risk of hypothy. If your cat was quarantined for more than 5-7
days, chances are he received a high dose. The quarantine period varies
from state to state, so, my estimate could be wrong.

You might want to call Radiocat and ask them how much his dose was and how
they determined the dose. The dose should have been determined by serum T4
concentrations- but some facilities have a 'one size fits all' dose. Most
of the cats I had treated received about 4 to 5 mCi- but some radio
facilities dose cats as high as 10-30 mCi.

You'll have a better idea of how long his hypothy might last once you find
out what his dose was.

Best of luck,

Phil

thomas.dometios@pb.com
November 1st 05, 07:50 PM
Phil, thanks for the info. One more question though. If he is hypo
after 3 months, is it still possible that it is transient or is that a
long time meaning that it could possibly be permanent.

Phil P. wrote:
> > wrote in message
> ups.com...
> > Has anyone had their cat swing hypothyroid after having the Radiocat
> > treatment? Our 10 year old cat had bloodwork 3 months after the
> > procedure and it showed that he is now hypothyroid. The Vet said this
> > happens sometimes but they usually don't treat it unless the symptoms
> > (excessive weight gain, lethargy, etc.) become really bad. He did go
> > from about 10.5 lbs in June to 11 lbs. 13oz. at the end of October. He
> > is sleeping a lot and doesn't really have much energy. I hope we don't
> > have to treat this since one of the reasons we had the procedure was to
> > eliminate the need to medicate him daily. Also, can the hypo. be
> > temporary/transient? Thanks.
>
> Yes it can - but it depends on the dose of I-131. If your cat received a
> large dose, hypothy could take longer to resolve or it could become
> permanent. Many
> cats go through transient hypothyroidism after radioiodine tx. -- it
> takes a little time for thyroid-stimulating hormone (TSH) secretion to kick
> in again and for the atrophied thyroid tissue to become functional again.
> Most cats don't require treatment unless they become symptomatic - which
> isn't common.
>
> Many radio facilities routinely administer high doses of I-131 to guarantee
> the destruction all the hyperfunctioning thyroid tissue in one shot. The
> high doses certainly accomplish that, all right, but they also greatly
> increase the risk of hypothy. If your cat was quarantined for more than 5-7
> days, chances are he received a high dose. The quarantine period varies
> from state to state, so, my estimate could be wrong.
>
> You might want to call Radiocat and ask them how much his dose was and how
> they determined the dose. The dose should have been determined by serum T4
> concentrations- but some facilities have a 'one size fits all' dose. Most
> of the cats I had treated received about 4 to 5 mCi- but some radio
> facilities dose cats as high as 10-30 mCi.
>
> You'll have a better idea of how long his hypothy might last once you find
> out what his dose was.
>
> Best of luck,
>
> Phil

Phil P.
November 2nd 05, 12:37 AM
> wrote in message
oups.com...
> Phil, thanks for the info. One more question though. If he is hypo
> after 3 months, is it still possible that it is transient or is that a
> long time meaning that it could possibly be permanent.

Sure, its possible his hypothy will become permanent- but its not probable.
Very few cats <5%) become permanently hypothy after I-131 tx- and that's
usually because the dose was too high.

I'll explain how I-131 works so you'll understand what's happening: The
I-131 is almost entirely concentrated in the hyperfunctioning (adenomatous)
thyroid tissue. The normal thyroid tissue is atrophied because it hasn't
been receiving TSH stimulation. Because the normal thyroid tissue is
suppressed, it only receives a very small dose of I-131. However, if the
cat received a large dose of I-131- the normal thyroid tissue receives a
higher dose of I-131, too. The more I-131 the normal tissue receives, the
longer it takes to begin functioning normally. If the initial dose of I-131
was too high- normal thyroid tissue can be destroyed too.

As far as 3 months being a long time to remain hypothy- I can't say for sure
because the hypothy period is relative to the dose of I-131 and I don't know
how high your cat's dose was. If he received a high dose- >10 mCi, then no,
3 months isn't a long time. T4 concentrations in the blood are usually
normal within 2 weeks of I-131 tx in about 70 to 80% of cats, and in over
90% of cats by 3 months. But as I said, a high dose can prolong the period
of hypothy or sometimes destroy normal tissue, too. The only thing you can
do is have him checked every few weeks and wait it out. If he develops
clinical signs of hypothy, call your vet immediately and don't wait for his
next scheduled re-check.

Sorry I can't be more helpful- this is one of those things that doesn't have
a clear cut answer.

Best of luck,

Phil.