A 75 kg female has gained about 20 pounds over the last four months; however, her impression that her neck has enlarged was worrisome and led her to seek medical attention. She reports tiring easily and feels mentally sluggish. Her friends indicate that her voice seems to be deepening.

Physical examination reveals puffy facies, delayed deep tendon reflexes, yellowish skin, and a firm, large thyroid.

Laboratory data: Total T₄ 3.8 ug/dL (5 - 11 ug/dL); RT₃U 26% (indirect measure of saturation of TBG binding sites, 26%-35%); TSH 22 uIU/ml (0.4-5 uIU/ml); ATgA 55% (< 10%; antibody to thyroglobulin measure);antimicrosomal by TRC aggutination 1:2800 (< 1:100; antibodies to microsomal antigens by TRC aggutination); RBC 3.2; Hematocrit (Hct) 33% (37%-48%, female); Hemoblobin (Hgb) 12 gm/dL (12-16 g/dL, female); mean corpuscular volume (MCV) 104 um3 (86-98 um3); RAIU at 24h was 6% (24 h: 15%-35%; 5 h: 5%-15%; radioactive iodine uptake test;iodine utilization by the gland after trace dose of ¹²³I or ¹³¹I .).