Clinical case

An 18-year-old man had a 2-week history of progressive left arm weakness. He had no history of seizures or learning disabilities and no relevant family history. On examination, there was mild (grade 4) weakness of the left arm and bilateral pyramidal signs. MR scan of brain (T2/fluid-attenuated inversion recovery (FLAIR)) showed bilateral hyperintense lesions in the centrum semiovale (figure 1A), with faint peripheral enhancement of the right-sided lesion with gadolinium (figure 1B). MR spectroscopy showed a decreased N-acetyl-aspartate peak. MR scan of the spinal cord was normal. Serum tests for HIV and syphilis, anti-aquaporin-4, anti-myelin oligodendrocyte glycoprotein and very-long-chain fatty acids were all negative. Adrenal function was normal. Nerve conduction studies found no peripheral nervous system involvement. …