Primary lateral sclerosis (PLS) is a rare neurological disorder. It may take several years for a doctor to diagnose PLS. While there’s no cure, treatments can help improve quality of life.

Primary lateral sclerosis (PLS) is a neurological disorder that affects adults and, in rare cases, children. More specifically, it’s a motor neuron disease that impairs a person’s ability to use voluntary muscles. Voluntary muscles are the muscles you use to walk, talk, eat, and perform everyday activities.

Keep reading to learn more about PLS, what causes it, and what treatments may help as the disorder progresses.

Signs and symptoms of PLS vary by person. Symptoms may develop slowly over time and often begin in the legs before developing in other parts of the body.

Symptoms may include:

  • muscle weakness, stiffness, and spasms
  • slow movement
  • trouble walking
  • balance issues
  • clumsiness
  • dysarthria (trouble forming words, slurred speech)
  • dysphagia (trouble swallowing and chewing)
  • bladder control issues
  • breathing issues

Researchers also share that people with PLS may have cognitive and behavioral changes. These may include issues with memory, social interactions, and mood.

We don’t know exactly what causes PLS. Most cases happen without any family history or other identifiable root cause.

In general, motor neuron diseases are caused by issues with the nerve cells that send information from the brain and spinal cord to the muscles in the body. When these messages are disrupted, a person’s control over their muscles is impacted, and they may have trouble with voluntary movements.

With adult-onset PLS, these issues typically begin somewhere between ages of 40 and 60. The disorder is slightly more common in people assigned male at birth than it is in people assigned female at birth.

Juvenile primary lateral sclerosis

Juvenile primary lateral sclerosis is caused by a gene mutation. In this case, it’s a mutation to the ALS2 or ERLIN2 genes that a child must inherit from both parents (autosomal recessive inheritance).

The ALS2 gene is responsible for producing a protein called alsin in the body that makes motor neuron cells function. When this protein is disrupted, it impacts a child’s voluntary muscle function.

Onset of juvenile PLS occurs when a child is between the ages of 2 and 11 years old. Just as with adult-onset PLS, juvenile PLS symptoms vary for each individual.

There’s no single test for PLS. Diagnosis is by exclusion of other diseases. For these reasons, diagnosis can be complicated and take some time. In fact, neurologists may wait at least 3 to 4 years to make a final diagnosis.

PLS also shares characteristics with other neurological disorders. For example, amyotrophic lateral sclerosis (ALS) is a neuromuscular disorder with similar symptoms, and in the early stages of PLS, symptoms may initially be mistaken for upper motor dominant ALS. It may take a doctor several years to distinguish PLS from ALS.

PLS may also initially be mistaken for hereditary spastic paraplegia.

Diagnosis may include:

  • Physical exam: This is done to observe movement changes, weakness, and spasticity.
  • Lab tests (blood tests): These are to rule out infection and other issues.
  • Magnetic resonance imaging (MRI): MRIs help medical professionals view the brain and spine.
  • Electromyogram (EMG): EMGs are done to evaluate muscle and lower motor neuron function.
  • Nerve conduction velocity (NCV): This is also known as a nerve conduction study.
  • Lumbar puncture: Also called a spinal tap, this is done to examine the cerebrospinal fluid.
  • Genetic testing: This can be helpful if juvenile primary lateral sclerosis is suspected.

Symptoms of PLS usually develop slowly, but progression varies by the individual. The disorder may progress over the course of a few years to a few decades.

You may notice symptoms in the leg muscles of one leg before the other. Over time, these sensations may spread to the arm muscles and bulbar muscles (those at the base of the brain). The disease may even progress to the muscles of the face or make breathing or swallowing difficult.

As PLS progresses, mobility and communication may become more difficult, which can also limit a person’s independence. That said, not everyone who has PLS will experience all the possible symptoms. And symptoms that do develop may not happen all at the same time.

There’s no cure for PLS. While the progression of symptoms can vary from person to person, it’s not always fatal, and people may have a normal life expectancy.

Treatment focuses on the symptoms a person is experiencing:

  • Various therapies: Certain therapies may be used to help with muscle weakness, joint mobility, and everyday tasks. They may include physical therapy, occupational therapy, speech therapy, and rehabilitation.
  • Medications: For example, muscle relaxants, such as baclofen, tizanidine, and benzodiazepines, can help with muscle spasticity. Pain medications, over-the-counter (OTC) or prescription, may help with discomfort. Antidepressants may help with depression.
  • Medical devices: Medical devices like canes, wheelchairs, braces, and speech synthesizers can help people manage mobility issues and regain some independence with everyday activities.

Clinical trials

Clinical trials are studies that allow researchers to examine conditions more closely, including underlying causes or potential treatments.

The United States Library of Medicine maintains an online database of clinical trials. For more information on previous trials and trials that are currently recruiting people with PLS, check out

Being diagnosed with a rare disorder can be difficult physically as well as emotionally. Many people experience a range of emotions and may also develop clinical depression.

If you’ve been diagnosed with PLS, reach out to your doctor to ask about support groups in your area. Groups may not be called “PLS groups” specifically. Instead, they may be under the umbrella of motor neuron disorders (MND).

Other resources include:

Make an appointment with your doctor if you experience sudden weakness or stiffness in your legs or other concerning symptoms, like trouble talking or swallowing.

Not all muscle issues or movement changes are related to motor neuron disorders. Even if yours are, it can take some time to be diagnosed with PLS. Your doctor can help you get treatment and different therapies to help with your symptoms while awaiting a diagnosis.