Clinical Reasoning: A 69-Year-Old Man With Rapid Cognitive Decline and Abnormal Movements

The differentials for rapidly progressive dementia are broad, encompassing structural, infectious, inflammatory, neoplastic, and neurodegenerative etiologies. The presence of abnormal movements further complicates the diagnostic approach. We describe a 69-year-old man presenting with a diverse array of neurologic symptoms, starting with rapidly progressive cognitive impairment, later developing abnormal movements, sleep disruption, and constitutional symptoms. Despite extensive investigations and empirical treatment, the diagnosis remained elusive until postmortem evaluation. This case highlights the challenges inherent in neurologic diagnostic odysseys, offering insight into the diagnostic reasoning process and unveiling novel clinical findings that may aid earlier recognition of this rare disorder.