An acute inflammatory condition of the nervous system that damages the lining of nerves (called the myelin sheath). The nerves of the body are essential and help control muscle contraction. In this disorder the nerves no longer normally transmit the impulses from the brain to the muscles causing weakness and paralysis of the muscles. Patients experience muscle weakness that begins in the legs and moves upward. The paralysis can prevent breathing and result in death. The exact cause of this disorder is not known but it is frequently associated with a viral infection such as a cold or flu.