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Primary Lateral Sclerosis (PLS)

Primary lateral sclerosis (PLS) is a progressive neuromuscular (nerves and muscles) condition that causes worsening muscle weakness and/or stiffness. Symptoms usually begin in your legs. Over time, weakness and stiffness spread to other muscles throughout your body.

Can PLS turn into ALS?

Early signs of ALS can look like PLS. PLS only affects your upper motor neurons (UMN) and ALS affects both your upper and lower motor neurons (LMN). You may receive a PLS diagnosis first if you only have symptoms that affect your UMN. Later, symptoms of ALS in both your UMN and LMN become apparent, so your healthcare provider may change your diagnosis to ALS.

Most cases that look like PLS are actually early stages of UMN-predominant ALS that eventually develop into ALS. For this reason, a diagnosis of PLS should only be made after you experience symptoms for at least three to four years.

PLS vs. ALS: What’s the difference?

Both primary lateral sclerosis (PLS) and amyotrophic lateral sclerosis (ALS) are neuromuscular conditions. There are differences between each.

PLS
ALS
Causes degeneration of upper motor neurons (UMN).
Causes degeneration of upper and lower motor neurons.
Symptoms include muscle stiffness, weakness and spasms.
Symptoms include muscle wasting (atrophy) and significant muscle weakness.
Slow progression of symptoms.
Fast progression of symptoms.
Less common than ALS.
More common than PLS.

Symptoms of PLS develop slowly. Some of the first symptoms you may notice are:

  • Muscle stiffness in your legs.
  • Muscle weakness in your legs.
  • Difficulty walking or maintaining your balance.
  • Muscle spasms or painful cramps.

As the condition progresses, other symptoms may include:

  • Muscle stiffness and weakness in your fingers, hands and arms.
  • Difficulty controlling your bladder (urinary urgency and incontinence).
  • Pain in your lower back and neck.

While rare, you may have symptoms that affect the muscles of your tongue. These can cause:

  • Slurred speech (dysarthria).
  • Difficulty swallowing (dysphagia).

We don’t know what causes most cases of PLS.

A change that happens in your DNA during conception causes a very rare form of PLS that affects children and teenagers (juvenile primary lateral sclerosis).

How does PLS affect my body?

PLS is a neuromuscular condition. It affects your nerves and muscles, specifically the motor neurons (nerve cells) in your brain and their fibers (projections) that extend from the cells to your spinal cord. These are also known as your upper motor neurons (UMN).

Normally, when you want to move your legs, your brain sends a message that passes to your spinal cord neurons along nerve fibers to the voluntary muscles (muscles under your direct control) in your legs. When your muscles get this message, they move.

PLS slowly breaks down the UMN (degeneration), so your muscles don’t get the messages they need to move as expected.

Is primary lateral sclerosis hereditary?

PLS isn’t hereditary. This means that it doesn’t pass down in your biological family. Cases usually happen randomly without a history of the condition in your family.

 

What are the risk factors for PLS?

Anyone can develop PLS. The average age of diagnosis is 50 years old. But the condition can affect people above or below age 50, including children. It’s more common among men.

As PLS progresses, you may have trouble walking without assistance. You might need to use a cane, a walker or a wheelchair. In addition, muscle weakness may make you more at risk of falls or accidents where you could injure your body if you lose balance.

 

A healthcare provider will diagnose PLS after a physical examination, a neurological examination and testing. They’ll review your symptoms to rule out look-alike conditions like ALS or multiple sclerosis. Diagnostic testing may include:

  • Blood tests.
  • Electrodiagnostic examination (nerve conduction and needle electrode studies), which measures how well your nerves and muscles are working.
  • Magnetic resonance imaging (MRI) of your brain and spinal cord.
  • A cerebrospinal fluid (CSF) analysis after a lumbar puncture (spinal tap) to look for abnormalities specific to neuromuscular conditions.

How is PLS treated?

Treatment for PLS helps you manage your symptoms and could include:

  • Medications to reduce muscle stiffness, spasms and difficulties swallowing.
  • Physical therapy to decrease muscle weakness, and improve muscle flexibility and joint range of motion.
  • Devices to assist with independence and mobility, like a cane, walker or wheelchair.
  • Speech therapy or devices to assist with speaking.

What medications treat PLS?

Common medications to treat symptoms of PLS include:

  • Baclofen and tizanidine for muscle stiffness.
  • Quinine for muscle cramps.
  • Diazepam to relax your muscles.

Are there side effects of the treatment?

Each medication may come with side effects that vary based on the type. Talk to your healthcare provider before starting a medication to learn more about the side effects.

Is PLS curable?

Unfortunately, there’s no cure available for primary lateral sclerosis.

What is the life expectancy for PLS?

PLS doesn’t directly affect your life expectancy. If you have PLS, you’ll have the same lifespan as someone without the condition.

What can I expect if I have PLS?

How fast your symptoms appear and worsen varies from person to person. On average, the progression of primary lateral sclerosis is slow and happens over many years or decades. If you notice a sudden worsening of symptoms, contact your healthcare provider.

Medications are effective in decreasing your symptoms and helping you go about your day without interruptions. For your safety, you may want to consider using a cane, walker or wheelchair to give you more independence and confidence when you move.

Can PLS be prevented?

As the cause isn’t known, there’s no way to prevent primary lateral sclerosis.

When should I see a healthcare provider?

Talk to your healthcare provider if you notice progressive changes to your muscles like stiffness or weakness. If you have a PLS diagnosis and a medication you take worsens your symptoms of gives you side effects, let your healthcare provider know.

What questions should I ask my healthcare provider?

If you have PLS, you probably have questions for your healthcare provider, such as:

  • Which treatments will help me manage my symptoms?
  • Are there side effects of the treatment?
  • How will I know if my condition is worsening over time?
  • What types of exercises can I do to help maintain muscle function?
  • Should I use a cane or walker?
  • Amyotrophic Lateral Sclerosis Society of Canada. Primary Lateral Sclerosis (PLS) (https://www.als.ca/wp-content/uploads/2017/04/ALSCAN-PLS.pdf). Accessed 9/11/2023.
  • National Institute of Neurological Disorders and Stroke (U.S.). Primary Lateral Sclerosis (https://www.ninds.nih.gov/health-information/disorders/primary-lateral-sclerosis). Accessed 9/11/2023.
  • National Organization for Rare Disorders, Inc. Primary Lateral Sclerosis (https://rarediseases.org/rare-diseases/primary-lateral-sclerosis/). Last reviewed 08/17/2007. Accessed 10/6/2023.
  • Spastic Paraplegia Foundation. About PLS (Primary Lateral Sclerosis) (https://sp-foundation.org/understanding-pls-hsp/pls.html). Accessed 9/11/2023.
  • The ALS Association. What Is ALS (https://www.als.org/understanding-als/what-is-als)? Accessed 9/11/2023.

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