A 75 year old man comes to you with gradual onset cognitive decline. A few years ago, he was encouraged to ramp his career down because of poor job performance. A year later, he started having driving difficulty, getting lost, misjudging distances, and failing to see other cars and stop signs. He had a cognitive evaluation which noted impairments in attention and executive and visuospatial function. His memory isn't impaired.
When you talk to his wife and children, they say that his cognitive impairment seems to have fluctuations. In fact, one time he "blanked out" so badly, he was brought to the emergency department. They ruled out stroke and seizure, and sent him home. He occasionally acts in a bizarre manner, has speech or motor arrest, or becomes really somnolent. The episodes have variable durations, and in between, he has pretty normal function. For a while, they thought he was just tired in the daytime, requiring long naps, but once he started having prolonged staring spells and speech disturbances, they became more concerned. In addition, the wife wonders if he's having visual hallucinations from time to time.
He has a family history of Parkinson's disease. He is a retired college professor. He reports no bad habits: no drinking, smoking, drugs, or even caffeine.
You perform a brief neuro exam and find that he has trouble copying overlapping pentagons, drawing a clock, subtracting serial sevens, and spelling WORLD backwards. On the rest of your exam, you note bradykinesia, limb rigidity, and an unusual gait. He has no tremor. His deficits are subtle and symmetric.
His MRI is the one on the left. The MRI on the right is a patient with a similar presentation but a different diagnosis.
Challenge: What do you think this is?
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