This 70-year-old right-handed woman presented with a 2-year history of slowly worsening cognition, then with more recent abrupt decline. She noted increasing difficulty recalling recent events and coming up with words. Over the last month, her family reported that she became slow in her thinking and easily confused. About a week prior to this assessment, she had been found on the floor unresponsive and taken to the emergency room, where she had a witnessed seizure. Metabolic abnormalities and infections were ruled out. A lumbar puncture showed elevated protein (80 mg/dl) but no other abnormalities. Her brain MRI without contrast showed asymmetric subcortical and periventricular T2 hyperintensities (Figure 45.1). She was started on levetiracetam 500 mg BID. Since then, she continued to decline but did not have further seizures. On examination, she exhibited bradyphrenia and fluctuating alertness.