A patient with rapid cognitive decline and visual failure

A previously healthy 63-year-old man was brought to the psychiatrist because of increasingly becoming withdrawn over a period of one month. He was noted to be cognitively impaired and blind and thus referred to the neurologist. His pupils were normal in size and reaction to light, and the optic fundi were normal. He was noted to have symmetrical bradykinesia and rigidity in his limbs. Diffusion-weighted magnetic resonance image (DWI) of his brain and part of his electroencephalogram (EEG) record are shown.