A 32-year-old woman presents with weight loss of 6.4 kg (14 lb) during the past 8 months and diarrhea of recent
onset. Menstruation had ceased 10 weeks earlier. She appears anxious, with pressured speech. Physical examination detects
baseline sinus tachycardia, sweaty palms, and a diffusely enlarged thyroid gland. Laboratory tests reveal a thyroid-stimulating
hormone (TSH) level of 0.00 µU/mL (normal, 0.45 to 4.5 µU/mL), a free thyroxine (FT4) level of 4.8 ng/dL (normal,
0.61 to 1.76 ng/dL), and a positive thyroid-stimulating immunoglobulin (TSI) level with high titer.