Block and replace for hyperthyroid for a second time because tsh staying suppressed

[Sal888]

I’ve had overactive problems for some years now, had block and replace which failed as I went hyper one year after, was on and of carbimazole and then was diagnosed hyper again in the last few months. last results were t4 24.6 tsh0.02. I’m currently taking 20mg of carbimazole, I Was at endo yesterday who informed me my tsh has been suppressed for a while now and they want to put me on block and replace again to try and raise my tsh levels. I’ve never heard of this being done I just thought block and replace was for hyper patients newly diagnosed with hyperthyroid? I don’t understand why my tsh is staying suppressed. Any advice I would be most grateful.

[MaisieGray]

"I don't understand why my TSH is staying suppressed"

There is a phenomenon known as hysteresis. In a 2016 paper by Melvin Khee-Shing Leow about hysteresis of the HPT axis, he describes it as a phase of prolonged suppression of TSH despite normalization of serum thyroid hormones over a variable period of time during the recovery of thyrotoxicosis; and that it serves as a buffering mechanism to reduce the magnitude of the biological impact of severe hyperthyroidism or hypothyroidism one the organism, especially when thyroid hormones escalate to extreme levels at either side of the normal. His paper concludes:

"The relationship of [FT4] and [TSH] is a reciprocal one best described by a negative exponential model. Hyperthyroidism and hypothyroidism lead to temporary suppression and overexpression of TSH out of the normal reference range. Even fluctuations of [FT4] within its normal reference range are associated with perceptible reciprocal changes in [TSH]. Mild displacements of [FT4] off the normal limits seldom result in any lagged recovery in TSH. However, in more extreme cases of hyperthyroidism or hypothyroidism, TSH is often appropriately suppressed or overexpressed for a protracted period of time despite adequate treatment that renders [FT4] into the normal range. This phenomenon is now recognized as hysteresis of the HPT axis and probably represents an adaptive response that confers a biological survival advantage for the organism. Hence, HPT axis hysteresis may be evolutionarily conserved and could well operate in vertebrates other than humans, as has been demonstrated in a mouse model. The implication of hysteresis acting as protective buffer may imply that rapid restoration of [TSH] to normal during this lagging recovery phase is not necessarily desirable or advantageous in terms of optimization of the euthyroid state compared to recovery of [TSH] along a slower trajectory."

[ling in reply to MaisieGray]

"The implication of hysteresis acting as protective buffer may imply that rapid restoration of [TSH] to normal during this lagging recovery phase is not necessarily desirable or advantageous in terms of optimization of the euthyroid state compared to recovery of [TSH] along a slower trajectory."

Wow, interesting stuff!

Thank you : )

[Lora7 in reply to MaisieGray]

My TSH (0.002) was suppressed for a couple of years and the Doctor didn't notice it even after numerous blood tests. When I was eventually treated my TSH rose to 9 which meant my dose of PTU was too high and I felt very ill. I blame my Doctor and Consultant for not monitoring me properly during that time. Against my Consultants advice I stopped PTU to see if my levels became normal again. I was lucky because I then went into remission for 4 years.

[ling]

Hi Sal, good to hear from you.

What happened to the RAI?

[Sal888 in reply to ling]

Hi ling in the end I opted out of RAI, now this is the next of it with block and replace which I had in the past several years back. Don’t know why they’ve decided to go down that route.

[ling in reply to Sal888]

Wow. Happy with the decision?

They want to try and raise your TSH. What are your blood test results? TRAb tested?

[Sal888 in reply to ling]

I’m happy I made the correct decision at this time in my life, I’ve several other issues going on and feel I made the right choice for now. Just tsh and t4 no other tests- t4 24.6 tsh 0.02 which I’m told hasn’t budged since early March.

[ling in reply to Sal888]

What are the ranges Sal?