Overview

Primary lateral sclerosis (also known as PLS) is a rare neurological condition which is part of a group of motor neurone diseases known as ‘lateral sclerosis’. This condition is generally caused by the degradation of the motor neurones within the brain and spinal cord that control body movement. It is characterised by weakness and stiffness of the muscles starting in the legs and then progressing to the hands and parts of the brain.¹

There is no specific test to diagnose PLS and the symptoms are quite similar to the other types of motor neurone disease.

Understanding neurological disorders

The nervous system

Have you ever wondered how the body reacts to and detects changes around us? The part of the body that creates a response to these changes is called the nervous system. Every living thing must respond to changes either in the environment or within itself to survive. These changes could occur due to light, temperature, or movement.

The Central Nervous System (CNS) includes the brain and spinal cord. This system is responsible for controlling the body's movement.

The Peripheral Nervous System include nerve cells (also called neurones). This system is responsible for carrying information to and from the CNS.

What are neurones? 

Neurones are long cells that carry information (in the form of electrical signals) along their length to the effector (an organ or cell that produces a response). As they are not always long enough, two neurones can meet each other via a tiny gap known as a synapse. The synapse allows the electrical signals to cross from one neuron to another until it eventually reach the effector.  

The role of neurones in movement

Motor neurones are nerve cells that carry electrical signals to effectors such as muscles. When there is a change in the environment that requires the body to move, a neurone from the spinal cord connects to a motor neurone to send signals to the effector which then produces a response through muscle contraction, resulting in a movement.

Neurodegenerative conditions

Neurological conditions are problems that affect the brain, spinal cord, and the nerve cells that make up the nervous system. They can affect anyone of any age. Research into the causes of neurological conditions is still ongoing, however, we do know that genetic factors, infections and trauma can play a role in their development.² It is estimated that around 1 in 6 people living in the UK are affected by neurological conditions, which illustrates the growing burden of these diseases on worldwide health.

One of the rare neurological (specifically motor neurone) conditions that will be talked about in this article is Primary Lateral Sclerosis (PLS). Now let’s dive into it!

Primary lateral sclerosis (PLS)

Primary lateral sclerosis is a rare neurological condition that is mostly known to affect the motor neurones that oversee muscle movement.¹ Therefore, a problem with these particular neurones causes the muscles to become weak and stiff. The exact cause of PLS is still unknown but the condition usually starts in the leg muscles and can spread to the arm muscles and then to the muscles at the base of the brain (called the bulbar muscles which handle speech, swallowing and chewing).² It can sometimes spread to the muscles of the face, but this is not very common.

Differentiating PLS from other neurological conditions

PLS occurs when the motor neurones in the part of the brain that handles motor function gradually degenerate causing body movements to be weak, slow, stiff, and requiring more effort to carry out. PLS is quite different from other neurological conditions as it usually takes a few years before it is finally diagnosed. This means that it can only be diagnosed after a neurologist has excluded other conditions by thorough testing. This may take up to 3-4 years or even a decade in some cases.⁴ 

Prevalence and demographics

PLS is more common in men than women with an average age of onset between the mid-40s and 60 years of age. ^2,4

Presentation

As aforementioned, the symptoms commonly start in the leg muscles and then spread to the body (trunk) followed by the arms, hands and then the bulbar muscles (at the base of the brain). It’s important to note that it can also start from the hand or tongue as well. As these muscles are mostly responsible for movement function, it’s no surprise that the symptoms of PLS mostly include weakness and stiffness with movement difficulty.⁴

Symptoms include:

• Muscle weakness
• Body stiffness
• Involuntary muscle spasms
• Slow movement
• Problems with balance
• Muscle cramping and clumsiness
• Difficulty walking
• Speech problems
• Swallowing issues
• Loss of bladder control

Diagnosis 

Diagnosing PLS is usually done by a neurologist who requests very expansive testing to exclude other neurological conditions with similar symptoms. Most specialists will have to monitor the gradual progression of your symptoms for at least three or four years before they can finally make a diagnosis. However, it is important to note that for some patients, the symptoms can quickly progress within a few years, therefore, you must speak to your doctor if you have these symptoms.³

Diagnostic tools

As there is no singular investigation to detect PLS, diagnosis usually involves excluding similar symptoms. Some of the tests your specialist might want to do include:^7,8

• Clinical Examination: This may involve observing movement and weakness changes
• Electromyography (EMG): Used to check your muscle and nerve cell function
• Magnetic Resonance Imaging (MRI): Involves capturing images of the brain and spine
• Blood tests: to rule out any infection or other related problems

Causes

The exact cause of PLS is still unknown and seems to occur randomly but the research into this is still ongoing. However, we do know that PLS is one of a group of diseases known as motor neurone conditions which are caused by a malfunction of the nerve cells within the brain and spinal cord.⁴

When a child between the ages of 2 and 11 years old inherits a gene mutation from either parent and unfortunately develops PLS symptoms, this is known as juvenile primary lateral sclerosis.

Management

Overview of current treatment options

Unfortunately, there are no treatments to prevent, cure or reverse PLS. Treatment for PLS mostly involves controlling the symptoms and preserving function by taking medications that act as muscle relaxants such as benzodiazepines. Other common medications used are baclofen and tizanidine which helps with muscle spasms, quinine for muscle cramps, and antidepressants to help with depression and provide emotional support.^5,8

Multidisciplinary approach 

Your doctor may also refer you for physical therapy to help with stiffness and speech therapy to help those affected with speech problems and facial muscle problems. Other healthcare professional programs that your doctor might refer you to include occupational therapy, and rehabilitation which can help you keep your independence whilst managing symptoms of slow movement, immobility, and muscle weakness.^6,7

You can also get support with your nutrition as well as medical support devices such as braces, canes, wheelchairs, and speech synthesisers (for communication).

Ongoing research 

As scientists are still working to find better ways to detect, treat and prevent disease, you could consider taking part in clinical trials to help advance our knowledge of PLS. For more information, visit NIH clinical research trials and you.

Impact on quality of life

For people who have PLS, it can be quite difficult both physically and emotionally as the people affected can go through a range of emotions due to the sudden change in their overall physical health. If you have been diagnosed, you should discuss your concerns or questions with your doctor.

PLS progression

Although there is currently no cure for PLS but there you’ll be glad to know that it is not fatal. The progression of symptoms varies between patients and certain people can maintain mobility, even without aid.

Support networks 

Having the support of family and friends can be of great help to individuals with PLS. It might also help to join a support group to learn how others are coping with the condition.

It is important to note that as PLS is not very common, finding a local support group can be quite difficult but some online discussion groups are available.

You should speak to your doctor and ask about any support group organisations as some of these groups might not be under the name “PLS” but could be under an umbrella name for PLS such as Motor Neurone Disease Organisation.

Summary

Primary Lateral Sclerosis (PLS) is a rare disease that is characterised by weakness and stiffness of the muscle that starts from the legs, followed by the hands and then the brain.

Whilst there is currently no cure for PLS, scientists are still working to find methods for early detection, treatment and prevention of PLS. Current treatments only act as supportive measures to maintain function which include medications, assistive devices and a multidisciplinary approach.