A 53-year-old man comes to the clinic due to progressive abnormal movement of the hands for the past several years. The patient first noticed both of his hands started shaking 3 years ago, and since then, the shaking has gotten worse. It occurs mainly when he reaches for objects, such as a glass of water or a magazine. The patient mentions that he had “shaky hands” in college when he studied for his finals and drank multiple cups of coffee. Medical history is non-contributory. The patient’s mother died from Alzheimer disease
complications at the age of 79, and his father died of myocardial infarction
at age 55. He recalls his father had a similar condition but cannot recall any details. Vitals are within normal limits. On physical examination, the patient is in no acute distress and no shaking is present at rest. When the patient is asked to outstretch his arms, a mild oscillating, flexion-extension
movement is noted bilaterally. Neurological examination, including gait, is within normal limits, except a positive finger
-to-nose test, which shows mild tremor
after reaching the target. Which of the following is the most likely diagnosis?