The disease is caused by a malfunction in the body's immune system that causes it wrongly to identify body cells as foreign invaders. As a result, the myelin sheath coating nerves in the brain and spinal cord is destroyed by mistake. Transmission between nerve cells slows down and becomes irregular, leading to loss of balance, reduced vision and bouts of localised paralysis. Eventually, patients may become totally paralysed and wheelchair-bound. Relapsing-remitting MS patients initially experience one or more bouts of illness, followed by complete or partial recovery.
Patients are clinically stable between relapses.
Progressive MS patients become gradually more disabled. The BBC is not responsible for the content of external internet sites.