Multiple Sclerosis Basics

Multiple sclerosis (MS) is a chronic immune-mediated disorder of the central nervous system. Inflammatory injury affects myelin and also damages axons and neurons in the brain, spinal cord, and optic nerves. Although demyelination is the feature that gives MS its name, neuroaxonal injury begins early; accumulated axonal loss helps explain why disability can eventually persist or progress even when a relapse has ended. Myelin normally allows an electrical signal to travel rapidly along a nerve pathway. When inflammation strips or disrupts myelin, conduction slows or fails. The location of the lesion determines the deficit: an optic nerve lesion may impair vision, a spinal cord lesion may cause leg weakness or bladder dysfunction, and a cerebellar or brainstem lesion may produce ataxia or diplopia. Multiple lesions in different locations create the variable pattern of MS. Inflammation that develops at different times produces relapses and remissions. Ongoing neuroaxonal degeneration contributes to progression between attacks or after years of relapsing disease. Epstein-Barr virus infection is currently the leading candidate causal factor; in a longitudinal cohort of more than 10 million US military recruits,...