A 50 year old right handed man presented with weakness of his right leg and arm of two months’ duration. The symptoms had come on over several days, during which he described a “dead leg” and he noticed his foot dragging while walking. On examination he had right lower limb pyramidal type distal weakness with a foot drop, power was graded at 4/5, and he had an upgoing plantar reflex. A computed tomogram of the brain showed a left parietal lesion with surrounding oedema but no midline shift, so contrast enhanced magnetic resonance imaging was undertaken (figs 1⇓ and 2⇓). Analysis of the cerebrospinal fluid showed raised protein with normal cell counts, normal angiotensin converting enzyme values, oligoclonal bands, IgG of 185 mg/L (normal value <40), and a negative viral polymerase chain reaction. Serum immunoglobulins and vitamin B12 values were normal; viral antibodies and antibodies for spirochetes were negative. He had no history of a neurological deficit. Fig 1 Axial fluid attenuation inversion recovery (FLAIR) magnetic resonance image at the level of the superior aspect of the lateral ventricles Fig 2 Contrast enhanced T1 weighted magnetic resonance image at the same level as fig 1 ### 1 What does magnetic resonance imaging show? #### Short answer The fluid attenuation inversion recovery (FLAIR) sequence shows multiple foci of periventricular high signal and a larger area of high signal in the left centrum semiovale (fig 1), which …