A 63 year old white man presented to the accident and emergency department with a 24 hour history of gradual onset of mild weakness of his left upper limb, which progressed to involve his left lower limb. There was no history of any other CNS symptoms. He also stated that the paresis varied with posture—being worse on standing and sitting, while it was relieved by lying down; it was also associated with a noticeably diminished short-term memory over the past few weeks. Clinical examination confirmed a mild left hemiparesis (grade 4/5), with brisk reflexes and an “equivocal” plantar response on …