Overview

Primary lateral sclerosis (PLS) is a type of motor neuron disease that causes the nerve cells in the brain that control movement to fail over time. PLS causes weakness in your voluntary muscles, such as those you use to control your legs, arms and tongue. You may experience movement problems, such as difficulty with balance, slow movements and clumsiness. You may eventually experience problems with chewing, swallowing and speaking.

This rare condition can develop at any age, but it usually occurs between ages 40 and 60 and is more common in males than females. A very rare subtype of PLS, known as juvenile primary lateral sclerosis, begins in early childhood and is caused by an abnormal gene passed from parents to children.

PLS is often mistaken for another, more common motor neuron disease called amyotrophic lateral sclerosis (ALS). While likely related to ALS, PLS progresses more slowly than ALS and in most cases isn't fatal.