Multiple sclerosis (MS): magnetic resonance image (MRI) of the brain of a woman aged 43 years suffering from multiple sclerosis. Demyelinating lesions, due to the destruction of the myelin sheath around the axons of nerve cells, appear as the bright circular regions towards the centre of the brain. The course of MS is characterized by recurrent relapses followed by remissions. MS may affect 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.