Definition

Primary lateral sclerosis (PLS) is a rare disease that causes progressive weakness in voluntary muscles such as in the legs, hands, and tongue. PLS is one of the diseases, along with amyotrophic lateral sclerosis (or Lou Gehrig's disease), that are grouped together as motor neuron diseases.

Description

Motor neuron diseases like primary lateral sclerosis develop because the nerve cells that normally control the movement of voluntary muscles degenerate and die. The disease is typically detected in middle age, after age 50. The symptoms of the disorder become progressively worse, with muscles typically affected in the following order: legs and feet, main part of the body (the trunk), arms and hands, and face....