My son is in the military and was diagnosed with graves disease. after an unsuccessful attempt to bring the thyroid under control he was given radiation to kill the thyroid. He is now on synthroid and after approx. 6 mnths was judged stable enough to return to active duty. Recently he was on maneuvers and the goiter reappeared.This was the first time he has done strenuous physical exercise since his initial diagnosis. Since the thyroid is presumably dead, what might be the causes for this reappearance?