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Primary lateral sclerosis

Primary lateral sclerosis is a rare neuromuscular disease with slowly progressive weakness in voluntary muscle movement. Primary lateral sclerosis belongs to a group of disorders known as motor neuron diseases.

Primary lateral sclerosis affects the upper motor neurons (also called corticospinal neurons) in the arms, legs, and face. It occurs when nerve cells in the motor regions of the cerebral cortex (the thin layer of cells covering the brain, which is responsible for most higher-level mental functions) gradually degenerate, causing movements to be slow and effortful.

The disorder often affects the legs first, followed by the body, trunk, arms, and hands, and finally the bulbar muscles (muscles that control speech, swallowing, and chewing).

Symptoms include:

  • Weakness
  • Muscle stiffness and spasticity
  • Clumsiness
  • Slowing of movement
  • Problems with balance and speech

Primary lateral sclerosis is more common in men than in women, with an onset that generally occurs between ages 40 and 60. Primary lateral sclerosis progresses gradually over a number of years, or even decades. Scientists do not believe primary lateral sclerosis has a simple hereditary cause.

The diagnosis of primary lateral sclerosis requires extensive testing to exclude other diseases. When symptoms begin, primary lateral sclerosis may be mistaken for amyotrophic lateral sclerosis or spastic paraplegia. Most neurologists follow an affected individual's clinical course for at least three to four years before making a diagnosis of primary lateral sclerosis.

Treatment is symptomatic. Muscle relaxants such as baclofen, tizanidine, and the benzodiazepines may reduce spasticity. Other drugs may relieve pain and antidepressants can help treat depression. Physical therapy, occupational therapy, and rehabilitation may prevent joint immobility and slow muscle weakness and atrophy. Assistive devices such as supports or braces, speech synthesizers, and wheelchairs may help some people retain independence. Speech therapy may be useful for those with involvement of the facial muscles.

Primary lateral sclerosis is not fatal. There is no cure and the progression of symptoms varies. Some people may retain the ability to walk without assistance, but others eventually require wheelchairs, canes, or other assistive devices.

How can I or my loved one help improve care for people with primary lateral sclerosis?

Consider participating in a clinical trial so clinicians and scientists can learn more about primary lateral sclerosis and related disorders. Clinical research uses human volunteers to help researchers learn more about a disorder and perhaps find better ways to safely detect, treat, or prevent disease.

All types of volunteers are needed—those who are healthy or may have an illness or disease—of all different ages, sexes, races, and ethnicities to ensure that study results apply to as many people as possible, and that treatments will be safe and effective for everyone who will use them.

For information about participating in clinical research visit NIH Clinical Research Trials and You. Learn about clinical trials currently looking for people with primary lateral sclerosis at

Where can I find more information about primary lateral sclerosis?

Information may be available from the following resources:

ALS Association
Phone: 800-782-4747


Spastic Paraplegia Foundation
Phone: 877-773-4483

Content source: Accessed June 29, 2023.

The information in this document is for general educational purposes only. It is not intended to substitute for personalized professional advice. Although the information was obtained from sources believed to be reliable, MedLink, its representatives, and the providers of the information do not guarantee its accuracy and disclaim responsibility for adverse consequences resulting from its use. For further information, consult a physician and the organization referred to herein.

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