I also was on lithium long before I was diagnosed with hypothyroidismSp? I had a fine needle biopsy done on the nodule that was on my thyroid and stuck out pretty much on the left side of my neck. I was told it was benine, and was put on levexoyl for life. Now there is hardly any thing left of nodule, it has been watched for two years. Doctors really don't know if it was linked to medications. I had a misscarriage just before it showed up. All that I have to worry about is if it gets larger again, then they would do another fine needle, other than that no problems. All I can suggest is that if is a worry to you they should do a fine needle. Wish I had more answers as to the causes, My daughter also has the same thing. Good luck and if you find out more than I know let me know!