DEFINITION:
Motor Neuron Disease is defined as an unequivocal diagnosis of one of the following : Amyotrophic Lateral Sclerosis (ALS or Lou Gehrig's disease), Primary Lateral Sclerosis, Progressive Spinal Muscular Atrophy, Progressive Bulbar Palsy, or Pseudo Bulbar Palsy.

INTERPRETATION:
Motor Neuron Disease is a rare progressive degenerative disorder which affects the central nervous system that controls muscular activity. As the nerves degenerate the muscles weaken and deteriorate. This definition identifies the five specific conditions covered, of which the most commonly recognized one is Amyotrophic Lateral Sclerosis (ALS), also known as 'Lou Gehrig's Disease'.