I have had twitching muscles since November 2001. They started shortly after beginning Synthroid. I have been on and off of different thyroid medications/supplements and the twitches have continued. Nothing seems to make them better or worse except they sometimes seem worse when I am more tired than usual, although not always. I have not been tested for them and don't know what they are from but have read that they can be caused by fibromyalgia, which I suspect I may have. I have been doing research on iodine and thyroid disease and have come across something called Iodorol, which I am about to try. I also came across (on the internet) a doctor named Dr. David Brownstein who treated his own thyroid problems with high doses of iodine and has done research and wrote a book about iodine deficiency. You may want to check it out on the internet. A web site I found was
www.quackcenter.com, which tells a lot about iodine and Dr. Brownstein. Hope this information helps you and hope it helps to know there are others who have twitching muscles too. I was scared of them at first too but I'm getting used to them and kind of ignore them now.