Primary lateral sclerosis (PLS)

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.

Symptoms Causes Complications

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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