A 56 year old man who had been diagnosed with multiple sclerosis six years earlier was admitted to the hospital with an acute change in mental state. He had collapsed at home and was unresponsive when rescue arrived. In the emergency room he had a depressed level of consciousness and difficulty following commands, with paucity of speech, dysarthria, and hypophonia. There was no evidence of head trauma. His blood pressure was 100/63 mm Hg and his temperature was 36.1°C.