amyotrophic lateral sclerosis

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A chronic, progressive disease marked by gradual degeneration of the nerve cells in the central nervous system that control voluntary muscle movement. The disorder causes muscle weakness and atrophy and usually results in death. Also called Lou Gehrig's disease.

Wiktionary

1. n. pathology, neurology A chronic, progressive disease characterized by degeneration of the central nervous system and the loss of voluntary muscle control.

WordNet 3.0

1. n. thickening of tissue in the motor tracts of the lateral columns and anterior horns of the spinal cord; results in progressive muscle atrophy that starts in the limbs