Review Question - QID 214378

A 75-year-old man is referred to a neurologist for "abnormal behavior." He is accompanied by his daughter who said that the patient had a fall approximately 1 week ago but did not injure his head and that his movements began to appear "slow" about 2 months ago. He has garbled speech and episodes of confusion where he does not know where he is. However, after these episodes he does return to his mental baseline - he knows where he is, his speech is intelligible, and he recognizes his family. The daughter endorses that the first episode of confusion happened about 1 year ago. At times, he appears agitated at things that the daughter does not see, and once asked her why there was a dog in the house, even though no one owns a dog. His mother had Alzheimer disease, and his father died due to myocardial infarction. Physical examination is notable for upper extremity limb rigidity and short-stepped and bradykinetic gait. Which of the following is most likely the diagnosis?