Sorry to hear this, always a challenge to have a serious diagnosis. Next step I dont know, but consider these facts;
Most people that had this diagnosis, never took Iodine at all.
It is an autoimmune condition, which can happen to any organ in our body, if something is wrong with the immune system. Lets say the immune system attack a joint; is the main minerals needed for the bones to be considered as the cause? Of course not.
Search, also the effect high vit D if you choose to take it. Also search the threads of hashimotos at this board.
Best of luck!