A 42 years old female presents with impaired gait and unexpected stumbling. She has become increasingly irritable and is having trouble completing assigned tasks on time at work. Her husband reports that she has become restless, pays less attention to her appearance and social obligations, and at times is anxious and upset. On examination, her speech is somewhat uneven and she is inappropriately flippant. She exhibits random “piano-playing” movements of the digits along with other movements of the limbs, torso, and face, and tandem walking is impaired. On neurological exam, she is unable to keep her tongue fully protruded for 10 seconds and her coordination is impaired. What is the most likely diagnosis?