Thyroidectomy and NDT - Does TRH/TSH feedback mechanism still apply with no thyroid?

Hi all,

Can anyone explain the following to me in layman's terms. My partner is on NDT and our approach as per STTM approach is to increase by half a grain every two weeks if he is feeling hypothyroid symptoms return. Once we hit the range 2 to 3 grains to increase more slowly, maybe 0.25 grain every two weeks.

However I came across the following in the STTM website:

"Being afraid to raise too quickly can result in a suppression of the feedback loop between the hypothalamus, pituitary and thyroid gland, i.e less messenger hormones are released, making you even more hypothyroid than you began (plus you may experience the results of extra adrenaline).."

I thought if you had had a thyroidectormy and on NDT that you were bypassing the TRH / TSH / T3/T4 loop altogether? i.e. when optimal your TSH is suppressed at about 0.4 and you should be aiming for Free T4 in midrange, Free T3 in upper range?

I understand the impact of adrenal functional, iron etc - but cannot get my head around the hypothalmus, pituitary and thyroid gland loop if you have no thyroid!!

Thanks in advance to anyone who can shed light!

14 Replies

  • Icoc, the feedback loop principle still works without a thyroid. It just relies on thyroid replacement to provide hormone instead of the thyroid. Pituitary gland senses circulating hormone and if it is low produces TSH to stimulate the thyroid gland to produce more hormone. If there is no thyroid to produce hormone TSH will continually rise unless thyroid hormone replacement is taken. When sufficient hormone is detected pituitary shuts down TSH.

    ThyCa patients awaiting RAI have to stop taking hormone until their TSH is >30 and can take up radioactive iodine. I'm thyroidless and a year ago I stopped thyroid meds for 4 weeks and TSH rose to 107.5. 2 months back on 100mcg T4 + 20mcg T3 TSH was 0.16.

  • Thanks Clutter - so when STTM refers to a negative feedback loop then I think they must be talking about a situation with a thyroid. There is no "loop" back in the thyroidless person as there is no thyroid to lower the T3 and T4 in response to a raised TSH, which would further cause the pituitary to pump out more TSH etc etc.

    So in my partner's case staying on a too low dose may mean his TSH will rise but this is really just a (bad) indirect measurement of where his free T4 and free T3 levels are at? Can i assume there is no negative feedback loop because the thyroid is gone? The raised TSH itself does not cause any action? or does it?

  • Icoc, Raised TSH indicates lack of circulating hormone ie undermedication in someone who is thyroidless.

    The pituitary and hypothalmus still function as part of the feedback loop even though the thyroid gland can't respond to prompts to produce more thyroid hormone. They will react to levels of thyroid hormone replacement. If there is insufficient thyroid hormone replacement TSH will rise and once restored will shut off when sufficient replacement hormone is detected.

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  • Ok thanks Clutter

  • In addition to the thyroid-hypothalamus-pituitary feed back loop there is another: best described as working between the pituitary (through TSH) and the conversion enzymes in the general body (the deiodinases that convert T4 to T3. When you have a thyroid there is a careful balance between the thyroid feedback and the tissue feedback. Lose your thyroid and the feedback is now restricted to

    the body tissues and the pituitary only. The problem is that on losing your thyroid altogether you can become unbalanced as regards T4/T3 supply and some people (not the majority but a strong minority) can't force their tissues to convert enough T4 to T3 to satisfy their requirements - thus you need either NDT or T3 additionally to T4 to satisfy your body requirements. This isn't true of everyone, and the more residual thyroid function you have the better T4 alone works.

  • Aah so to clarify - once the tsh goes up is the impact at the tissue level that it reduces the ability to convert t4 to t3? is the biological reason for this that the body in detecting a scarcity of t4, starts reducing the use of t4 in the non essential cells?

    So by not increasing quickly enough on ndt, the tsh increases, this causes a reduction in t4 to t3 conversion, making you more hypo and thus increasing the tsh further and so on?

    Or have I made a few incorrect assumptions here?

  • High TSH stimulates T4-T3 conversion in the tissues (in the same way as it promotes T4/T3 production in the thyroid). Losing the thyroid removes that source of hormones. If substituting only by T4 by mouth, some people cannot take in enough T4 to produce enough T3 in the tissues for health. Even when TSH is suppressed they still cannot make enough T3. The additional problem is that when TSH is suppressed the T4-T3 conversion in the tissues is also suppressed to its minimum so that such people simply cannot use T4 only as therapy. They have to have some form of T3 direct as well to overcome this problem.

  • Diogenes, every time you give us another tidbit, it just makes me more anxious for the full paper. PR

  • I become terribly ill and over medicated, by following that advise. I would be very cautious with that website and their ideas.

  • Hi faith63 - I would be very keen that he avoids this. Can I ask you to elaborate a bit and hopefully we could use your learning a to avoid it?

    1. Did you have a full thyroidectomy?

    2. When increasing your dose were you checking temps in the a.m. - we are finding his waking temp hovers 96.6 to 96.8 which is indicative of hypo?

    3. How quickly did you increase your dosage on armour - and what were you switching from. My husband was on 125 mcg levothyroxine and is now on 2 grains armour after about

    4. Were you getting blood tests every month? Is that how you knew you were over medicated?

    5. My understanding was that if you found yourself over medicated that you just reduce your dosage I.e go back a step or if severe enough go back to 1 grain and start again. Did this not reduce your symptoms effectively?

  • At point 3 he's gone from 125 mcg to 2 grains armour in about 5 weeks

    Week 1: 1 grain

    Week 2 & 3: 1.5 grain

    Week 4 & 5: 2 grains

    We're going to try and hold on 2 grains to week 6 or 7 to see what the build up feels like to him. But surely if his temps drop again below 96.5 and he's sleeping all day it means we should increase?

  • sttm, really pushes the belief that without desiccated, you will not become well, and you need to get to about 3 grs..well, ndt, flares up my Hashi's and 3 grains would have killed me. I get hyper symptoms on very small doses of that, but not t3 only. Because of that website, i poisoned myself, 3x on ndt, believing that i wouldn't ever feel better and that the rest of my organs would suffer due to not taking it. Several very well know docs, say people with Hashi's should not take ndt.

    I wish i could answer your other questions.. I finally found that i do best with no t4 containing meds, but i am still not ok.

  • Thanks for your response - I suppose this probably might not apply to my partner as he doesn't have hashimotos and no longer has a thyroid. Sorry ndt did not work for you and you are still struggling to be optimal

  • People with no thyroid can be poor converters of t4 and do well on t3 only.

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