Primary lateral sclerosis (PLS), which belongs to the group of motor neuron diseases, is a rare neuromuscular disease characterized by progressive muscle weakness in the voluntary muscles, such as those you use to control the legs, arms and tongue. PLS only affects upper motor neurons and it is a type of motor neuron disease that causes muscle nerve cells to slowly break down, causing weakness.

Primary lateral sclerosis can happen at any age, but it usually occurs between ages 40 and 60. Primary lateral sclerosis is often mistaken for another, more common motor neuron disease called amyotrophic lateral sclerosis (ALS). However, primary lateral sclerosis progresses more slowly than ALS, and in most cases is not fatal.



The symptoms of PLS usually take years to progress and the hallmark of PLS is progressive weakness and spasticity of voluntary muscles. The first symptoms are often stiffness, spasticity, tripping or difficulty with the balance and lifting the legs. Other people may be the first to notice a change in the affected person’s gait. Few other symptoms that are experienced by the patients include:

  • Weakness and stiffness progressing to the trunk, then the arms, hands, tongue and jaw. ;
  • Hoarseness, reduced rate of speaking, slurred speech and drooling as the facial muscles weaken;
  • Drooling and difficulties with swallowing and breathing late in the disease
  • Occasionally, some patients suffer from speaking and swallowing difficulties



The cause of adult primary lateral sclerosis is unknown. In most cases, it is not an inherited disease, and it is not known why or how it begins. Juvenile primary lateral sclerosis, on the other hand, Juvenile primary lateral sclerosis is an autosomal recessive disease, meaning that both parents have to be carriers of the gene to pass it to their child, even though they do not have the disease themselves. Juvenile PLS is caused by mutations in a gene called ALS2. Although researchers do not understand how this gene causes the disease, they know that the ALS2 gene is responsible for giving instructions for creating the alsin protein, which is present in motor neuron cells. When the instructions are changed, the alsin becomes unstable, which in turn impairs normal muscle function.



The rate at which symptoms will progress and how severe they will become is impossible to predict. Although the average progression lasts around 20 years, the disease has highly variable effects from person to person. Some people may be able to continue to walk, but others will eventually need to use wheelchairs or other assistive devices. Adult PLS is not thought to shorten life expectancy, but it may gradually affect the quality of the life as more muscles become disabled. Weaker muscles may cause you to fall more, which may result in injuries.