A 48-year-old right-handed man presented to a district general hospital accompanied by his wife. Since childhood he had had migraine with visual aura. Over the last few years he had continued to experience his usual auras infrequently but these were now seldom followed by headache and readily managed with simple analgesia. He was in excellent health, although perhaps exercising less than he had previously. He was not taking any regular medication, did not smoke or drink alcohol excessively, and he had no family history of note.

On the day of presentation, he had been cycling to work when he developed his typical visual aura, but he continued cycling. After a few minutes he reached the security entrance. At that stage he noticed that his right arm was not quite right and he had difficulty swiping his security pass. He felt vaguely disorientated and was unable to greet the security officer. After parking his bicycle he climbed up the stairs to his office. On the way, he tried to greet a colleague but could not reply with anything beyond “yes” and “no” and so he feigned exhaustion. He sat down in his office chair about 15–20 minutes after the onset of his symptoms and for the first time noticed that he had marked weakness of his right arm. When his boss entered he again had difficulty speaking, although he could understand perfectly well. He went to the medical centre where the staff called an ambulance. An hour later his symptoms had all but resolved and by the time he reached the hospital emergency department he was back to normal. The first year medical resident documented a normal neurological and general examination. He was transferred to the CT scanner where he again noted right arm weakness. The weakness lasted about 5 minutes …