A 17-year-old woman presents with symptoms of a fine tremor of her hands. The tremor is best seen when her hands are stretched out. She is not on any medications and reports no alcohol use. Which of the following is the most likely diagnosis?

In hyperthyroidism, neurologic symptoms include tremors of the hands, exophthalmos, lid lag, stare, and muscle weakness. Muscle weakness of hyperthyroidism affects the pelvic girdle and, to a lesser extent, the shoulder girdle. Reflexes are normal or increased, and sensation is normal. It must be differentiated from myasthenia gravis, which may also accompany thyrotoxicosis.