Primary Lateral Sclerosis (PLS) Symptoms and Treatment

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 in the fifth decade of life. It is not known how many people in the world are affected by PLS, but it is very rare.

A woman experiencing leg pain
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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.


The diagnosis of primary lateral sclerosis includes specialized nerve testing called EMG (electromyography) and nerve conduction studies. 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.


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 the 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


Primary lateral sclerosis brings progressive disability and loss of function but does not affect the mind or shorten the lifespan 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.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Organization for Rare Disorders. Primary lateral sclerosis.

  2. National Institute of Neurologic Disorders and Stroke. Primary lateral sclerosis information page.

  3. Lau FS, Brennan FP, Gardiner MD. Multidisciplinary management of motor neurone disease. Aust J Gen Pract. 2018;47(9):593-597. doi:10.31128/AJGP-02-18-4495 

  4. Spastic Paraplegic Foundation, Inc. About PLS (Primary Lateral Sclerosis).

  5. Spastic Paraplegia Foundation, Inc. Treatments and therapies.

Additional Reading

By Mary Kugler, RN
Mary Kugler, RN, is a pediatric nurse whose specialty is caring for children with long-term or severe medical problems.