multiple sclerosis

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A chronic autoimmune disease of the central nervous system in which gradual destruction of myelin occurs in patches throughout the brain or spinal cord or both, interfering with the nerve pathways and causing muscular weakness, loss of coordination, and speech and visual disturbances.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun pathology A chronic disease of the brain and spinal cord characterized by changes in sensation, visual problems, weakness, depression, difficulties with coordination and speech, impaired mobility and disability.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a chronic progressive nervous disorder involving loss of myelin sheath around certain nerve fibers