What is Primary Lateral Sclerosis?

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  • Written By: Mary McMahon
  • Edited By: Kristen Osborne
  • Last Modified Date: 28 October 2018
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Primary lateral sclerosis (PLS) is a rare disease involving damage to the upper motor neurons responsible for regulating voluntary movement. Patients with this condition experience increasing muscle stiffness and lack of muscle control. This disease should not be confused with amyotrophic lateral sclerosis (ALS), a similar condition involving both upper and lower motor neurons where the muscles usually atrophy over time as a result of loss of neurological function.

This condition usually onsets over the age of 50, and it is progressive, growing worse over time. Patients might notice signs like clumsiness and stiffness before developing slurred speech, difficulty walking, and trouble with fine motor tasks involving the hands. PLS is not generally fatal, with patients dying of other causes before the neurological degeneration progresses to the point where it would become life-threatening. This is an important distinguishing feature separating it from ALS.

In an even more unusual condition called juvenile primary lateral sclerosis, patients develop this condition at a young age as a result of inheriting a faulty gene. People with a family history of neurological diseases like primary lateral sclerosis can be at increased risk of passing on deleterious genes to their children, leading to a variety of congenital conditions, including juvenile primary lateral sclerosis. People concerned about this risk can consult a genetic counselor.


Diagnosis of primary lateral sclerosis can be challenging, as there is no specific test doctors can use to see if people have it. Symptoms are evaluated and patients can be tested for other diseases to rule out other known causes of those symptoms. Sometimes, ALS and PLS are confused at diagnosis, explaining why some people believed to have ALS live longer than expected and experience less severe symptoms, because they actually have primary lateral sclerosis instead.

Medications can help patients with muscle stiffness and pain associated with this condition. Physical therapy may also be recommended to develop as much strength and dexterity as possible. Eventually, patients may need mobility aids and other assistive devices to get around, and they can also benefit from speech therapy to address issues like trouble swallowing and unintelligible speech. Many patients also find it helpful to attend psychotherapy or patient support groups as part of the adjustment process of getting used to the diagnosis and learning to live with the condition. This can be traumatic, especially for people who have lived very active lives, and people may experience grief and complex emotions after diagnosis.



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