A 37-year-old woman presents to your office, complaining of unintentional weight loss, increased appetite, irregular menses and difficulty sleeping. Over the past 2 months, she has lost approximately 10 lb without changing her diet or activity level. Upon further questioning you learn that she has palpitations, intolerance to heat, nervousness, and tremors. Her husband has told her that she is quite irritable lately. Her coworkers at work noted that she looks very agitated and less productive at work. Her past medical history is significant for vitiligo and anxiety disorder. Her temperature is 100.1 °F, heart rate is 108 beats/min, blood pressure is 148/94 mm Hg, respirations are 19 breaths/min, and oxygen saturation is 96% on room air. When she looks at you, she seems to stare, and her eyes are somewhat protuberant. Her skin is moist and warm with marks of scratching. She has irregular depigmented patches on her hands and around her mouth, consistent with a history of vitiligo. Thyroid gland is diffusely enlarged with a soft texture and a well-delineated border. It is nontender and an audible bruit is present. On cardiac examination, you note tachycardia and widened pulse pressure. Neuromuscular examination is significant for a fine resting tremor when she spreads her fingers, a shortened relaxation phase in deep tendon reflexes and proximal muscle weakness. Her pregnancy test is negative. Her serum TSH level is 0.03 mIU/L (0.4 – 4.0 µg/mL). You suspect primary hyperthyroidism in this patient. What is the most common cause of primary hyperthyroidism in the United States?
