Most doctors reckon that it is better for patient to be hypothyroid that hyperthyroid; so they normally recommend radioiodine therapy to kill off the thyroid gland and then manage the " hypo " condition with thyroxin. As long as your condition is stabilised and your blood tests indicate normal T3/T4 hormone levels, I suppose you can fly as a flight crew. If not, class 1 medical will be denied. Hope this helps but mind you, I am not an AME !