Mayo Clinic Health Library

Primary lateral sclerosis (PLS)

Updated: 07-12-2013

Definition

Primary lateral sclerosis (PLS) causes weakness in your voluntary muscles, such as those you use to control your legs, arms and tongue. Primary lateral sclerosis is a type of motor neuron disease that causes muscle nerve cells to slowly break down, causing weakness.

Primary lateral sclerosis can happen at any age, but it usually occurs between ages 40 and 60. A subtype of primary lateral sclerosis, known as juvenile primary lateral sclerosis, begins in early childhood and is caused by an abnormal gene passed from parents to children.

Primary lateral sclerosis is often mistaken for another, more common motor neuron disease called amyotrophic lateral sclerosis (ALS). However, primary lateral sclerosis progresses more slowly than ALS, and in most cases isn't fatal.

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Symptoms

Signs and symptoms of primary lateral sclerosis (PLS) usually take years to progress. They include:

  • Stiffness, weakness and spasticity in your legs
  • Tripping, difficulty with balance and clumsiness as the leg muscles weaken
  • Weakness and stiffness progressing to your trunk, then your arms, hands, tongue and jaw
  • Hoarseness, reduced rate of speaking, slurred speech and drooling as the facial muscles weaken
  • Difficulties with swallowing and breathing late in the disease

Less commonly, PLS begins in your tongue or hands and then progresses down your spinal cord to your legs.

When to see a doctor
Make an appointment to see your doctor if you have persistent problems with stiffness or weakness in your legs, or with swallowing or speaking.

If your child develops involuntary muscle spasms or seems to be losing balance more often than usual, make an appointment with a pediatrician for an evaluation.

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Causes

In primary lateral sclerosis (PLS), nerve cells in the brain that control movement fail over time. This loss causes movement problems, such as slow movements, balance problems and clumsiness.

Adult primary lateral sclerosis
The cause of adult primary lateral sclerosis is unknown. In most cases, it's not an inherited disease, and it's not known why or how it begins.

Juvenile primary lateral sclerosis
Juvenile primary lateral sclerosis is caused by mutations in a gene called ALS2.

Although researchers don't understand how this gene causes the disease, they know that the ALS2 gene is responsible for giving instructions for creating a protein called alsin, which is present in motor neuron cells.

When the instructions are changed in someone with juvenile PLS, the protein alsin becomes unstable and doesn't work properly, which in turn impairs normal muscle function. Adults who get primary lateral sclerosis don't appear to have the same gene mutation.

Juvenile primary lateral sclerosis is an autosomal recessive disease, meaning that both parents have to be carriers of the gene to pass it to their child, even though they don't have the disease themselves.

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Complications

Although the average progression of primary lateral sclerosis (PLS) lasts around 20 years, the disease has highly variable effects from person to person. Some people may be able to continue to walk, but others will eventually need to use wheelchairs or other assistive devices.

Adult PLS isn't thought to shorten life expectancy, but it may gradually affect the quality of your life as more muscles become disabled. Weaker muscles may cause you to fall more, which may result in injuries.

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Tests and diagnosis

There is no single test that confirms a diagnosis of primary lateral sclerosis (PLS). In fact, because the disease can mimic signs and symptoms of other neurological diseases such as multiple sclerosis and ALS, your doctor may order several tests to rule out other diseases.

After taking a careful record of your medical history and family history and performing a neurological examination, your doctor may order the following tests:

  • Blood work. You'll have blood tests to check for infections or other possible causes of muscle weakness.
  • Magnetic resonance imaging (MRI). An MRI or other imaging tests of your brain or spine may reveal signs of nerve cell degeneration.

    Your doctor also may order an MRI to look for other causes of your symptoms, such as structural abnormalities, multiple sclerosis or spinal cord tumors.

  • Electromyogram (EMG). During an EMG, your doctor inserts a needle electrode through your skin into various muscles. The test evaluates the electrical activity of your muscles when they contract and when they're at rest.

    This test can measure the involvement of lower motor neurons, which can help to differentiate between PLS and ALS.

  • Nerve conduction studies. These tests use a low amount of electrical current to test and measure your nerves' ability to send impulses to muscles in different areas of your body. This test can determine if you have nerve damage.
  • Evoked potentials. Electrodes, which are attached to your scalp and several other areas of your body, measure and record your brain's response to touch or muscle stimulation. These tests may help evaluate nerve damage or degenerative nerve conditions.
  • Spinal tap (lumbar puncture). In this procedure, your doctor uses a thin, hollow needle to remove small samples of the cerebrospinal — surrounding the brain and spinal cord — fluid from within your spinal canal for laboratory analysis. A spinal tap can help rule out multiple sclerosis, infections and other conditions.
  • Positron emission tomography (PET). A PET scan may reveal degenerative changes in the brain and help diagnose PLS.

After other diseases are ruled out, your doctor may make a preliminary diagnosis of PLS.

Sometimes doctors wait three to four years before giving a diagnosis, because early amyotrophic lateral sclerosis (ALS) can look just like PLS until additional symptoms surface a few years later. You may be asked to return for repeat electromyography testing over three to four years before the PLS diagnosis is confirmed.

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Treatments and drugs

The treatments for primary lateral sclerosis (PLS) focus on relieving symptoms and preserving function. There are no treatments to prevent, stop or reverse PLS. Treatments include:

  • Medication. Your doctor may prescribe medication to relieve muscle spasms (spasticity), such as baclofen, tizanidine (Zanaflex) or clonazepam (Klonopin). These medications are taken by mouth (orally).

    If your spasticity isn't controlled with oral medication, your doctor may recommend surgically implanting a medication pump to deliver baclofen directly to your spinal fluid (intrathecal baclofen).

    If you experience depression, your doctor may prescribe antidepressants. Amitriptyline and other drugs also can help drooling problems.

  • Physical therapy. Stretching and strengthening exercises may help to maintain muscle strength, flexibility and range of motion, and to prevent joint immobility. Heating pads can help relieve your symptoms of muscle pain.
  • Speech therapy. If your facial muscles are affected by PLS, speech therapy can help you compensate for speech and facial muscle problems.
  • Assistive devices. You may be evaluated periodically by physical or occupational therapists to determine whether you need assistive devices, such as a cane, walker or wheelchair, as PLS progresses.
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Lifestyle and home remedies

Although there's no cure for primary lateral sclerosis, you can make a few lifestyle choices to preserve muscle function for as long as possible:

  • Stay active. Continue activity or exercise programs as long as you can comfortably and safely do so. Staying active may help you keep your existing function and slow the progression of the disease.

    Be sure you stay safe, keeping in mind that your muscle weakness puts you at higher risk of tripping and falling.

  • Eat a healthy diet. Because PLS can cause your activity level to slow down, be sure you're eating a nutritious diet to avoid excessive weight gain and added pressure on your joints.
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Coping and support

Periods of feeling down about having primary lateral sclerosis are expected and normal. Dealing with the reality of an incurable, progressive disease can be challenging. To cope with the disease and its effects, consider these tips:

  • Seek emotional support. Family and friends can be great sources of comfort and support when you're wrestling with the emotional aspects of long-term disease.

    Because primary lateral sclerosis is an uncommon diagnosis, it might be a challenge to find a local support group for people with your condition. However, some online discussion groups are available, and it may be helpful to see how others have coped with the disease.

  • Get professional help if you need it. When faced with a chronic illness, it's not unusual to become overwhelmed at times. Seek out professional counseling for another perspective, or if you're struggling with depression and need advice on treatment.
  • Know and use resources available to you. If you reach a point where your disease is restricting your activities significantly, ask your doctor about devices designed to help you stay independent.

    In addition, there are social services available to people with disabilities of all kinds. Try to learn all you can about the resources available to you. Sometimes relying on your community for help can strengthen ties in new ways.

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