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What is thyrotoxic myopathy... just wondering?

Hello everyone,

Does anyone know whether it is possible to get thyrotoxic myopathy once the thyroid gland has been removed or partially removed, after many years?

Had partial thyroidectomy in 1980 (had a 4 nodule goitre and was told post operation i had papillary carcinoadenoma). No pre op scan in those days... not even since.

Was put on thyroxine and it appears i did "fairly well" for quite a while. Also not in best of health as I then developed rheumatoid arthritis and other autoimmune problems. Am taking 100 mcg and 75 mcg T4 on alternate days.

Have become rather ill for past 2 years or so and after a long battle with my GP and thanks to the very good advice from members of the HU Forum (many thanks to all of you - you know who you are xx) I have been prescribed B12 injections since beginning of February which have made quite a difference (although not yet totally 100%). However it appears i have become hyperthyroid (probably have been for quite a while but only got tested for TSH!!!! so that would explain why my test came back as "within normal range" each time).

Did ask GP to request further test back in December 2016;

TSH: 0.85 miu/L (0.3 - 5.5)

FT4: 23.1 pmol/L (12 - 22)

FT3: 3.8 pmol/L (3.1 - 6.8)

Thyroid Peroxidase antibody: 18 ku/L ( < 34.0)

Blood was drawn at 8 am, fasting and 24 hours after taking thyroxine, only drank water.

I understand I am a poor converter. Do not understand the TPantibody: 18 ku/L and the range of < 34.0... does that indicate I am ok or does it mean I am well above the range since it says less than 34.0.... bit confusing. Perhaps Rod will know?

My GP had previously said I was euthyroid but at my last appointment when pressed agreed I was hyperthyroid.... and we 'll discuss this at my next appointment.

I am quite weary about consulting an endocrinologist as they do not seem, on the whole, to know a great deal about the complex working or lack of, of thyroid... If anyone knows of a good endocrinologist then I would appreciate if you would email me privately. Thanks for that.

Looking forward to hearing from you with your good advice and support, as always.

Best wishes.

8 Replies


I think you are confusing high FT4 and possible over medication of Levothyroxine with hyperthyroidism.

Thyrotoxic myopathy (TM) is a neuromuscular disorder that develops due to the overproduction of the thyroid hormone thyroxine. Also known as hyperthyroid myopathy, TM is one of many myopathies that lead to muscle weakness and muscle tissue breakdown. Evidence indicates the onset may be caused by hyperthyroidism.[1] There are two known causes of hyperthyroidism that lead to development thyrotoxic myopathy including a multinodular goiter and Graves' disease. Physical symptoms of TM may include muscle weakness, the breakdown of muscle tissue, fatigue, and heat intolerance.[2] Physical acts such as lifting objects and climbing stairs may become increasingly difficult.[3] If untreated, TM can be an extremely debilitating disorder that can, in extreme rare cases, lead to death. If diagnosed and treated properly the effects can be controlled and in most cases reversed leaving no lasting effects.


Your FT4 is mildly over range but that doesn't mean you are over medicated as TSH is low, but not suppressed, and FT3 is low. Some patients need FT4 slightly over range in order to produce sufficient T3. You are a poor converter because although TSH is low and FT4 high your FT3 is low. If your Levothyroxine dose is reduced to bring FT4 into range your FT3 will drop lower.

Read Treatment Options in thyroiduk.org.uk/tuk/about_... Email louise.roberts@thyroiduk.org.uk if you would like a copy of the Pulse article to show your GP.

Your TPO antibodies are 18 which is below 34 so you don't have autoimmune thyroiditis (Hashimoto's).

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JGBH "What is thyrotoxic myopathy..."

I hadn't heard of it so I googled: brainfacts.org/diseases-dis...

"Thyrotoxic myopathy is a neuromuscular disorder that may accompany hyperthyroidism (Graves' disease, caused by overproduction of the thyroid hormone thyroxine). Symptoms may include muscle weakness, myalgias (muscle tenderness),............."

So if you have no thyroid gland then you can't be hyperthyroid, you would probably be being treated for hypothyroidism so I suppose the question is can over medication cause it? I don't know the answer to that so wont guess.

You haven't become hyperthyroid, you can't be if you have hypothyroidism, but you can be over medicated. This shows when FT3 is over range and your results don't indicate that :

TSH: 0.85 miu/L (0.3 - 5.5)

FT4: 23.1 pmol/L (12 - 22)

FT3: 3.8 pmol/L (3.1 - 6.8)

Your TSH is in range, your FT4 is slightly over range, and your FT3 is VERY low.

From ThyroidUK's 'Treatment Options':

"According to the BMA's booklet, "Understanding Thyroid Disorders", many people do not feel well unless their levels are at the bottom of the TSH range or below and at the top of the FT4 range or a little above.

Dr Toft states in Pulse Magazine, "The appropriate dose of levothyroxine is that which restores euthyroidism and serum TSH to the lower part of the reference range - 0.2-0.5mU/l.

In this case, free thyroxine is likely to be in the upper part of its reference range or even slightly elevated – 18-22pmol/l. Most patients will feel well in that circumstance.

But some need a higher dose of levothyroxine to suppress serum TSH and then the serum-free T4 concentration will be elevated at around 24-28pmol/l.

This 'exogenous subclinical hyperthyroidism' is not dangerous as long as serum T3 is unequivocally normal – that is, serum total around T3 1.7nmol/l (reference range 1.0-2.2nmol/l)."

Dr Toft is past president of The British Thyroid Association and leading endocrinologist. You can obtain a copy of the article by emailing louise.roberts@thyroiduk.org.uk to show to your doctor.

What you need is some T3 added to your Levo to increase your FT3, and a reduction in Levo to bring your FT4 down.

"Do not understand the TPantibody: 18 ku/L and the range of < 34.0... does that indicate I am ok or does it mean I am well above the range since it says less than 34.0...."

Your antibodies are less than the upper limit of negative (<34 = less than 34 as you know), so you're not positive for autoimmune thyroid disease. However, there are two types of antibodies TPO - Thyroid Peroxidase - which has been tested, and TG - Thyroglobulin - which the NHS never seem to do. You can be negative for one and posit for the other.


Thank you SeasideSusie. Very informative as usual, and reassuring.



Sorry to hear you're still feeling rough, but at least your battle for B12 shots was successful! As you know, it may take a while for the full effects of those to be felt.

I agree with Clutter and SeasideSusie that you are not over-medicated for hypothyroidism - quite the reverse. You may find an increase in levo makes you feel better, but if you don't convert well, then maybe the next option to try would be NDT, or an addition of liothyronine/T3 to your levo.

B12 deficiency/PA (sorry, I can't remember whether you have confirmed PA), hypothyroidism, RA and any other AI conditions can all conspire to make you feel very poorly. What are you taking for the RA?

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Hi Hillwoman,

Thank you for replying to my post. As you will probably see I "reposted" a correction to my previous post whereby I made a typo error, stating "hypo" when in fact it should have been "hyper" (mildly perhaps).

For RA after years of taking many many drugs (ruined my stomach lining!) I am now on weekly self injections of Enbrel (etanercept) which have made my life more liveable.... but of course like any anti body TNF drugs there are side effects but worth taking as it allows to live a better quality of life...

Not sure about PA yet.... but having gastroscopy on Thursday with biopsies taken so hope to know a little more soon. However I must have been B12 deficient (and for quite a time) as the injections have made a big difference, so that is proof of B12 deficiency although my B12 levels were about mid range and I my IF antibody test (intrinsic factor for antibodies in stomach) was negative. Both these test are unreliable but sadly taken very seriously by medical professionals.... as we all know only too well.

Am due to discuss hyperthyroidism with GP nest month.... but don't want to make too many changes that may throw my thyroid function up into the air and could make me feel even worse. If only endocrinologists were any good with understanding of thyroid dysfunction treatments.


I have to admit, I don't feel as if I'm the brightest lamp in the street at the mo, so I may well have missed something. :-)

Your FT3 is horribly low, and as such you can't really be over-medicated (as opposed to being hyperthyroid). FT3 is the only essential measurement, and the others just help give a more detailed picture.

Good luck with the anti-TNF treatment. I understand there are risks with it, but also that it can be the only therapy that makes a difference for many people. I've had success so far with LDN, but my RA was in the early stages, so that might be a significant factor.

All the best for the gastroscopy and I hope it yields some useful information.


This thyroid business is complicated.... and my GP, like many others, does not appear to understand it either. Lots of thinking to be done then... and thank goodness for all the very good advice from members of the forum.

Glad you're happy with your treatment for RA. my RA was extreme and extremely debilitating, having spent a year in hospital when it first started in the 80s.

Thanks for your good wishes for the gastroscopy.

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If your taking B12 supplements are you also taking vitamin B complex to keep all the B's balanced.

Have you had levels of vitamin D, folate & ferritin checked

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