Long thyroid stimulating agent is

Answer is option 2, antibody to thyroid receptors. Thyrotropin receptor (TSHR) antibodies that stimulate the thyroid (TSAb) cause Graves' hypehyroidism and TSHR antibodies which block thyrotropin action (TBAb) are occasionally responsible for hypothyroidism. Unusual patients switch from TSAb to TBAb (or vice versa) with concomitant thyroid function changes. We have examined case repos to obtain insight into the basis for "switching."