Primary lateral sclerosis (PLS)

Overview

Primary lateral sclerosis (PLS) is a rare condition that affects the nerve cells in the brain that control movement. PLS slowly breaks down nerve cells and causes weakness in the leg, arm and tongue muscles. It is a motor neuron disease that makes it harder to control voluntary muscle activity such as speaking, walking, breathing, and swallowing.

Symptoms typically begin with balance trouble. People with PLS may move slowly and bump into or drop things. Over time, symptoms may include trouble with the hands and arms, followed by issues with chewing, swallowing and speaking. Less commonly, issues with speaking and swallowing may be the first symptoms.

This condition can develop at any age, but usually happens between the ages of 40 and 60. PLS also can begin in early childhood, although this is not common. PLS in children is known as juvenile primary lateral sclerosis. Juvenile PLS is caused by changes in a gene passed from both parents to a child. PLS is more common in people who are assigned male at birth.

PLS is often mistaken for another, more common motor neuron disease called amyotrophic lateral sclerosis (ALS). While PLS is likely related to ALS, PLS gets worse more slowly than ALS. In most people, PLS isn't fatal.

Symptoms

Symptoms of primary lateral sclerosis usually take years to develop and get worse. Symptoms generally begin in the legs. It is not common, but PLS symptoms can begin with weakness in the tongue or hands, then slowly move down the spinal cord to the legs. Symptoms may be different for everyone. These are common symptoms.

• Stiffness, weakness and muscle spasms in the legs. This is known as spasticity. Spasticity may start in only one leg and move to the arms, hands, tongue and jaw.
• Slow movement.
• Tripping and having trouble with balance.
• Bumping into or dropping things.
• Slow or slurred speech, a hoarse voice, and drooling.
• Trouble chewing and swallowing.
• In some people, frequent, rapid and intense shifts in emotions.
• Rarely, breathing and bladder issues late in the disease.

When to see a doctor

Make an appointment to see a healthcare professional if you have lasting stiffness or weakness in your legs or arms. Also see a healthcare professional if you have trouble swallowing or speaking.

Take your child to a healthcare professional if your child develops muscle spasms or seems to be losing balance more often than usual.

Causes

In primary lateral sclerosis, the nerve cells in the brain that control movement slowly break down and stop working. These nerve cells are called upper motor neurons.

As a result, the nerves are not able to activate the motor neurons in the spinal cord, which control voluntary muscles. This loss causes issues with movement. People with PLS may have trouble with balance, weakness, slowed movement and clumsiness. PLS also may affect speech and swallowing.

Adult-onset primary lateral sclerosis

The cause of PLS that begins in adulthood is not known. In most people, the disease is not inherited. It's not known why or how it begins.

Juvenile primary lateral sclerosis

Juvenile PLS is linked to changes in a gene called ALS2. The condition also has been linked to ERLIN2.

Researchers don't understand how these genes may cause the disease. But they know that the ALS2 gene instructs cells to create a protein called alsin. Alsin is present in motor neuron cells. These instructions are changed in someone with juvenile PLS, which causes the protein alsin to become unstable and not work as it should. This affects the function of the muscle.

Juvenile PLS is an autosomal recessive inherited disease. This means both parents have to be carriers of the gene to pass it to their child. Parents may not have symptoms of the condition, but if they both have the gene for the condition, they can pass it down to their child.

Risk factors

There are no known environmental or gene risk factors for adult primary lateral sclerosis. Genes may play a role in juvenile PLS, but researchers are still working to understand exactly how.

Complications

It can take as long as 20 years for primary lateral sclerosis to become worse. Symptoms vary from person to person. Some people continue to walk, but others eventually need wheelchairs or other assistive devices.

For most people, adult-onset PLS isn't thought to shorten life expectancy. But it can gradually affect the quality of your life as more muscles become disabled. Weaker muscles can cause you to fall, which can result in injuries. Trouble with chewing and swallowing may result in poor nutrition. Performing activities of daily living, such as bathing and dressing, may become hard.

People with PLS may develop trouble with their thinking, known as cognitive decline. Or they may have changes in their behavior. In some people, symptoms overlap with symptoms of frontotemporal dementia. Frontotemporal dementia is a form of dementia that also leads to changes in behavior and language skills.