Movement Disorders USMLE Step 1 Practice Question

A 35-year-old woman presents with a 5-year history of progressive tremor affecting both hands that worsens when she reaches for objects or attempts fine motor tasks such as writing. She reports that 2-3 alcoholic drinks markedly improve her symptoms for several hours. She denies family history of neurologic disease, head trauma, or toxic exposures. Vital signs are normal. On examination, she exhibits a regular, rapid tremor of the outstretched hands that increases with intentional movement and posturing. Strength is 5/5 throughout, reflexes are normal and symmetric, and gait is steady. Brain MRI shows normal architecture with no evidence of atrophy or structural lesions. Laboratory studies including TSH, free T4, ceruloplasmin, and 24-hour urine copper are all normal. Which of the following is the most likely diagnosis?