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, that are grouped...
Diagnosis is based on the observance of the muscle weakness and the progressive worsening of the weakness. The diagnosis can be delayed because the disease is mistaken for ALS.
Motor neuron diseases like primary lateral sclerosis develop because the nerve cells that normally control the movement of voluntary muscles degenerate and die.