APA Dictionary of Psychology

a disease of the central nervous system (brain and spinal cord) characterized by inflammation and multifocal scarring of the protective myelin sheath of nerves, which damages and destroys the sheath and the underlying nerve, disrupting neural transmission. The initial symptom of MS is often a visual disturbance, such as blurred or double vision, red–green color distortion, or blindness in one eye. Later symptoms include fatigue, weakness in the hands and feet, numbness, stiffness or muscular spasms, muscle and back pain, difficulties with coordination and balance, loss of bladder or bowel control, and depression. Some individuals also experience cognitive impairments, such as difficulties with concentration, attention, memory, and judgment. The onset is usually between the ages of 20 and 40, and, with periods of remission, the disease may continue for 25 years or more. Rapid progression to death is rare. The cause of MS, which occurs twice as frequently in females as in males, is unknown. However, the destruction of myelin may be due to an autoimmune response (see autoimmunity).