This 65-year-old right-handed woman presented with a 2-year history of worsening gait and short-term memory impairment. She first noticed slowness in her movements and impaired balance resulting in falls, mostly backward. She tried levodopa titrated to 1200 mg a day with no benefit. Over the previous year, she developed difficulties multitasking and was easily distracted. She endorsed difficulty swallowing and, more recently, urinary incontinence. Her husband noted that she was withdrawn and seemed to have lost interest in hobbies and in social interactions with the family. She denied depression, anxiety, cognitive fluctuations, or hallucinations. She endorsed decreased sense of smell and a history of dream enactment behaviors. On neurological exam, she was easily distractible and tangential. Her speech was hypophonic. Her extraocular eye movements were normal. There was symmetric bradykinesia and distal hand myoclonus when the arms were held outstretched. She was unable to walk unaided (Video 23.1). The Montreal Cognitive Assessment (MoCA) score was 18/30, with impairments in trail making, cube copying, and clock drawing, backward digit span, serial sevens, sentence repetition and delayed recall (she recalled one word freely and recognized the other four when multiple choices were given).