Primary Lateral Sclerosis


Primary lateral sclerosis (PLS) is a form of motor neuron disease that primarily affects the nerve cells in the brain responsible for controlling voluntary movements. In PLS, the degeneration of these nerve cells leads to muscle weakness in areas such as the legs, arms, and tongue.

The initial symptoms often involve difficulty with balance, leading to slow and clumsy movements. As the disease progresses, individuals may experience increasing difficulties with hand and arm coordination, followed by challenges in chewing, swallowing, and speaking. In some cases, the disease may start with issues related to speech and swallowing.

PLS can occur at any age but is most commonly diagnosed between the ages of 40 and 60. It tends to be more prevalent in men than in women. A rare form of the disease, known as juvenile primary lateral sclerosis, can begin in early childhood and is linked to a genetic mutation inherited from both parents.

Often confused with amyotrophic lateral sclerosis (ALS), another type of motor neuron disease, PLS progresses more slowly and is generally not life-threatening. Although related to ALS, PLS and ALS differ significantly in their impact and progression rates.


Symptoms of primary lateral sclerosis (PLS) generally develop slowly and worsen over time, often beginning in the legs. In rare cases, symptoms may start with weakness in the tongue or hands before progressing to the legs. Symptoms can vary significantly between individuals, but commonly include:

  • Spasticity: This involves stiffness, weakness, and muscle spasms in the legs. Spasticity may initially affect only one leg and can eventually spread to the arms, hands, tongue, and jaw.
  • Movement issues: Movement may become slower, and individuals might experience tripping, clumsiness, and balance problems.
  • Hand coordination: Difficulty with fine motor skills and general clumsiness of the hands may occur.
  • Speech and swallowing difficulties: Symptoms can include a hoarse voice, slowed or slurred speech, drooling, and problems with chewing and swallowing.
  • Emotional changes: Some individuals may experience frequent, rapid, and intense emotional shifts.
  • Other late symptoms: Rarely, breathing and bladder problems may develop in the later stages of the disease.

Consult a healthcare professional when:

  • Adults: Consult a healthcare professional if you have persistent leg or arm stiffness or weakness, or if you encounter difficulties with swallowing or speaking.
  • Children: Take your child to a healthcare provider if they develop muscle spasms or seem to lose balance more frequently than usual.


Primary lateral sclerosis (PLS) is defined by the progressive degeneration of the brain’s motor nerve cells responsible for controlling movement.
Most cases of primary lateral sclerosis has no known cause.

  • Adult-onset primary lateral sclerosis: This condition is typically not inherited. The reason behind its onset remains unclear.
  • Juvenile primary lateral sclerosis: PLS in children is a hereditary autosomal recessive condition. This implies that for a gene to be passed on to a kid, both parents must be carriers. Mutations in the ALS2 gene are the cause of juvenile PLS.

The ALS2 gene provides instructions for making a protein known as alsin, which is found in motor neuron cells. In individuals with juvenile primary lateral sclerosis, alterations in these instructions result in unstable alsin protein that does not function correctly. This instability affects muscle function. However, experts are uncertain on how this particular gene leads to PLS.

Risk factors

Primary lateral sclerosis can occur in individuals of any age, although the average age of diagnosis is around 50 years old, with cases reported in both younger and older individuals, including children. It is also observed to be more prevalent in males. Additionally, there are no known environmental factors that have been definitively linked to the development of PLS.