Multiple sclerosis. Coloured magnetic resonance imaging (MRI) scan of an axial section through the brain of a 48 year old 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. A lesion of demyelination (yellow) is seen at upper right. Lack of myelin around a nerve fibre reduces its ability to transmit signals. This leads to symptoms ranging from tingling and numbness to paralysis and death, depending on the nerves 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.