Share this article on:

By the Numbers: Primary Lateral Sclerosis

doi: 10.1097/01.NNN.0000351332.19274.d9
Department: the Waiting Room

Primary lateral sclerosis (PLS) is caused primarily by degeneration of the upper motor neurons in the brain and spinal cord. When those neurons stop working, muscles become weak as well as spastic or stiff, reflexes become hyperactive, and maintaining balance becomes difficult. There are also lower motor neurons in the spinal cord, which are spared in PLS.

PLS is often referred to as a benign form of amyotrophic lateral sclerosis (ALS). In PLS, because only the upper motor neurons are affected, the muscles don't atrophy or waste away as in ALS. While more than half of ALS patients die within three to five years of diagnosis, PLS patients can live for up to 20 years with the disease.

There is no cure for PLS. One or more drugs to control tight, spastic muscles are usually prescribed along with assistive devices such as walkers or wheelchairs. Speech therapy is effective for those who have difficulty talking.


The year that Dr. Jean-Martin Charcot of France first encountered a patient who had severe spasticity but no muscle wasting. After the patient's death, the autopsy revealed extensive scarring in the spinal columns (involving the upper motor neurons)—what we now call PLS.


The number of people in the U.S. who have PLS. Some doctors think the incidence rate may be as high as 2,000 because PLS is so difficult to accurately diagnose.


The median age of onset for PLS. The disorder usually begins in the legs, but it may also start in the tongue or the hands.


The average number of years it takes before a person is definitively diagnosed with PLS.


Number of active PLS studies currently listed on

Source: theSpastic Paraplegia Foundation (

Copyright © 2009, AAN Enterprises, Inc.