Multiple sclerosis. Magnetic resonance image (MRI) scan of an axial section through the brain of a patient with multiple sclerosis (MS). The eyeballs are seen at top; regions of the cerebrum of the brain are at left, right, and lower frame within the cranium. Inside the brain (centre) are a number of lesions caused by MS. These lesions are due to the destruction of myelin sheaths around nerve fibres. Progressive destruction of myelin in the brain and spinal cord produces such symptoms of MS as unsteady gait, tremor, speech defects, paralysis and incontinence. MS is thought to be an autoimmune disorder. No cure is yet known.