Multiple sclerosis. Coloured computed tomography (CT) scan of an axial section through the brain of a multiple sclerosis (MS) patient. The front of the brain is at top. In MS, the myelin sheaths that surround nerve fibres become damaged and destroyed. Two lesions of demyelination (red) are seen at upper left and centre right. Lack of myelin around a nerve fibre dramatically reduces its ability to transmit signals. This leads to symptoms ranging from tingling and numbness to paralysis and death, depending on which nerves are affected. The cause of MS is unknown, although it may be an autoimmune disorder (where the body attacks its own tissues). There is no cure.