Primary Lateral Sclerosis (PLS): A Progressive Motor Neuron Disease

Symptoms and Treatment Options for Primary Lateral Sclerosis

senior woman with leg pain
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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, causing painless but progressive weakness and stiffness of the muscles.

It is not known why PLS occurs, or exactly how the nerve cells are destroyed.

Primary lateral sclerosis seems to begin after 40 to 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 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 progression of PLS varies from case to case—Some may progress rapidly within a few years or slowly over a few decades.

Initial Symptoms. In many cases, the first symptom of PLS is muscle weakness and stiffness in the lower limbs. Other initial symptoms include:

  • One leg is usually affected more than the other, with slow progression to the other leg
  • Slow, stiff movements of the legs because of involuntary muscle spasms (spasticity)
  • Difficulty walking and maintaining balance, such as tripping or stumbling
  • Cramping of the affected muscles
  • General clumsiness

​Progressive Symptoms. Affected individuals may have increasingly more difficulty in walking. The use of a cane or similar device to assist in walking may be required.  In some cases, other symptoms may precede the development of muscle weakness in the legs.

Other symptoms may include:

  • Muscle spasms in the hands or at the base of the brain.
  • Painful muscle spasms in the legs, back, or neck
  • Trouble moving the arms and doing tasks such as combing hair or brushing teeth
  • Difficulty forming words (dysarthria) or speaking
  • Difficulty swallowing (dysphagia)
  • Loss of bladder control late in the course of primary lateral sclerosis

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 manifest similar symptoms, PLS is often confused with ALS.

Treatment of Primary Lateral Sclerosis

There is no cure at the moment for PLS, so treatment is focused on relieving the symptoms of the disorder. Treatment for PLS includes:

  • Medications such as Baclofen and Tizanidine to reduce muscle spasms
  • Drug treatment to address loss of bladder control
  • Physical and occupational therapy to help reduce spasms, improve mobility, and provide devices to help with walking and eating
  • Speech therapy to aid with speaking 
  • Orthotics and shoe inserts to relieve gait and foot problems

Support for Primary Lateral Sclerosis

Primary lateral sclerosis brings progressive disability and loss of function but does not affect the mind or shorten the life span of patients directly. For this reason, support groups such as the Spastic Paraplegia Foundation for patients and their families is key to adapting to the physical and emotional burdens of the disease. 


National Institute of Neurological Disorders and Stroke. NINDS Primary Lateral Sclerosis Information Page. 

Spastic Paraplegia Foundation. About PLS. 

Spastic Paraplegia Foundation. Treatments and Therapies.

National Organization for Rare Diseases. Primary Lateral Sclerosis. 

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