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updated October 16, 2010

Primary lateral sclerosis (PLS)

Filed under: Brain & Nervous System
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, which causes muscle nerve cells to slowly die, causing weakness.

Primary lateral sclerosis can happen at any age, but it's more common after age 40. 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 considered fatal.

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Signs and symptoms of primary lateral sclerosis typically 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 the tongue or hands, and then progresses down the spinal cord to the 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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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, on the other hand, has an identifiable cause: mutations in a gene called ALS2. Although researchers don't completely understand how it causes the disease, they know that the ALS2 gene is responsible for providing instructions for making a protein called alsin, which is abundant in motor neuron cells. When the instructions are altered in someone with juvenile PLS, the protein alsin becomes unstable and doesn't function 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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Although the average progression of primary lateral sclerosis 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 wheelchairs or other assistive devices for mobility or other activities.

Adult PLS isn't considered 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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There is no single test that confirms a diagnosis of primary lateral sclerosis. In fact, because the disease can mimic signs and symptoms of other neurological diseases such as multiple sclerosis and ALS, several tests are done to rule out other diseases.

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

  • Blood work. Blood tests are done to check for infections or other possible causes of muscle weakness.
  • Magnetic resonance imaging (MRI) of your brain and spine. An MRI or other imaging tests may reveal signs of nerve cell degeneration and look for other causes of your symptoms, such as structural abnormalities, spinal cord compression, multiple sclerosis and spinal cord tumors.
  • Motor and sensory nerve conduction studies. These tests use a low amount of electrical current to test how quickly your nerves carry impulses through your body, and can indicate damage to nerve cells.
  • Electromyogram (EMG). During this test, the doctor inserts a needle electrode through your skin into various muscles. The electrical activity of your muscles is evaluated 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.
  • Cerebrospinal fluid analysis. An analysis of your cerebrospinal fluid, which is taken during a lumbar puncture in your lower back, can help to rule out multiple sclerosis and other causes of spasticity.

After other diseases are ruled out, your doctor may make a preliminary diagnosis of PLS. Sometimes doctors wait three to four years before being sure of the 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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The treatments for primary lateral sclerosis focus on relieving symptoms and preserving function. There are no treatments to prevent, stop or reverse PLS. Treatments include:

  • Medication. Drugs are available to relieve muscle spasms (spasticity), including baclofen, tizanidine (Zanaflex), diazepam (Valium) or clonazepam (Klonopin). These medications are taken 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).

    Other medications may be prescribed to treat cramps or pain related to spasticity, including phenytoin (Dilantin) or analgesics.

  • Physical therapy. Stretching and strengthening exercises will help to maintain muscle strength, flexibility and range of motion, and to prevent joint immobility. Massage or therapeutic whirlpools also may provide relief from PLS symptoms.
  • Speech therapy. If your facial muscles are affected by PLS, speech therapy can help you compensate for the effect on your speaking patterns.
  • 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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Although there's no cure for primary lateral sclerosis, there are a few lifestyle choices you can make 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 will help you keep your existing function and slow the progression of the disease. Just 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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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 ways you haven't considered.

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