Case history

A 33-year-old man was brought by ambulance to the emergency department from a local park with a right-sided headache and amnesia. He did not know his name, age, address, occupation or marital status. He could not remember how he came to be in the park, nor could he recall any autobiographical event before that morning. Despite this alarming deficit, he responded to all questions directly, showing surprisingly little distress at his predicament. Cognitive testing showed that he was orientated to time and place, and able to perform well on tests of attention, concentration and recall. He was afebrile, and his physical examination was unremarkable. We observed no signs of head trauma or substance intoxication or withdrawal. His blood alcohol concentration was 0 and a urinary drug screen was unremarkable. A white cell count showed mild neutrophilia, but all other haematological and biochemical indices were normal. Cerebral computed tomography and lumbar puncture …