Light micrograph of human nervous tissue (white matter) in disseminated (multiple) sclerosis (MS), a demyelinating disease in which the main feature is the destruction of the myelin sheath that surrounds axons in the central nervous system. In this image, unaffected myelin in white matter appears dark blue; the demyelinated area remains unstained and appears light blue. The course of MS is characterized by recurrent relapses followed by remissions. MS affects different parts of the brain & spinal cord, a fact reflected in the range of symptoms, which include unsteady gait, limb tremors, involuntary eye movements & speech defects. Viral infection is a suspected cause.