An 80-year-old man is brought to the clinic by his daughter due to progressive difficulty walking over the past six months. She describes his gait as slow and unsteady, with frequent falls. He has also developed urinary incontinence and mild memory problems. On examination, he has a wide-based, shuffling gait and difficulty initiating movement. Mental status testing shows mild cognitive impairment. MRI of the brain shows ventricular enlargement without significant cortical atrophy. Which of the following is the most likely diagnosis?
