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Primary Lateral Sclerosis

Progressive motor neuron disease


Updated February 19, 2009

The nervous system is affected in PLS

The nervous system is affected in PLS

Photo © A.D.A.M.
Primary lateral sclerosis (PLS) is a progressive degenerative motor neuron disease. PLS affects the nerve cells in the body that control voluntary movement of muscles, called motor neurons. Over time, these motor neurons lose their ability to function.

It is not known why PLS occurs, or exactly how the nerve cells are destroyed. Primary lateral sclerosis seems to begin after 50 years of age. It is not known how many people in the world are affected by PLS, but it is very rare.

Symptoms of Primary Lateral Sclerosis

The loss of the nerve cells causes muscles to become stiff and difficult to move. Typically, the muscle problems start in the legs and move up the body to the trunk, arms, and muscles in the face and neck. The disease progresses slowly, usually over a few years.

Symptoms may include:

  • Difficulty walking, such as tripping or stumbling
  • Difficulty speaking or swallowing
  • Trouble moving the arms and doing tasks such as combing hair or brushing teeth
  • Painful muscle spasms in the legs, back, or neck
The symptoms slowly get worse over time.

Diagnosis of Primary Lateral Sclerosis

There is no specific test for primary lateral sclerosis, so most of the time the diagnosis occurs as the result of eliminating other possible causes of the symptoms. Because amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease) is more well known, and because the two diseases often appear similar, primary lateral sclerosis is often confused with it.

Treatment of Primary Lateral Sclerosis

There is no specific treatment or cure for primary lateral sclerosis, so treatment is focussed on relieving its symptoms. Medications such as baclofen and tizanidine can reduce muscle spasms. Physical, occupational, and speech therapy can also help reduce spasms, improve mobility, and provide devices to help with walking, talking, and eating.

Support groups such as the Spastic Paraplegia Foundation can help individuals and their families adapt to the physical changes the disease brings. Primary lateral sclerosis brings progressive disability and loss of function but does not affect the mind or shorten the life span directly.


"NINDS Primary Lateral Sclerosis Information Page." Disorders A-Z. 14 Feb 2007. National Institute of Neurological Disorders and Stroke. 15 Feb 2009

"PLS General Information." Disorders. Spastic Paraplegia Foundation. 15 Feb 2009

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