Primary Lateral Sclerosis – Symptoms and Causes

Overview

Primary lateral sclerosis (PLS) is a rare neurological condition that affects movement and muscle control. It is considered a slowly progressing motor neuron disorder and primarily impacts the upper motor neurons responsible for voluntary movement.

Although it shares some symptoms with other neurological diseases, such as ALS, PLS typically progresses more slowly and has a distinct clinical course. Early recognition and ongoing support play key roles in improving quality of life.

Signs and Symptoms

Primary lateral sclerosis (PLS) develops slowly, with symptoms often appearing gradually over months or years. Most people first notice problems with their legs and walking.

PLS typically begins with stiffness and weakness in the legs. People may stumble more often or feel like their legs are heavy when climbing stairs. Walking becomes increasingly difficult as muscle stiffness increases.

As the condition progresses, symptoms may spread to affect other body areas:

• Muscle Stiffness and Spasticity: Muscles become increasingly tight and resistant to movement.
• Weakness: Gradually developing weakness, particularly in the legs.
• Balance Problems: Difficulty maintaining stability when standing or walking.
• Slowed Movements: Tasks take longer to complete.
• Difficulty with Fine Motor Skills: Problems with buttons, writing, or other detailed hand movements.

Speech and swallowing problems often develop as the disease advances. Many people experience:

• Slow, slurred speech
• Difficulty chewing or swallowing
• Excessive drooling due to reduced ability to swallow saliva

Some people with PLS may also develop emotional changes, including inappropriate laughing or crying that doesn’t match how they actually feel. This is called pseudobulbar affect.

PLS rarely affects breathing or cognitive function. Most people maintain their thinking abilities throughout the disease course.

When to See a Medical Professional

Contact your doctor if you notice unusual muscle stiffness, weakness, or other symptoms that worsen over time. Early diagnosis helps manage primary lateral sclerosis (PLS) effectively.

Seek immediate medical attention if you experience:

• Sudden muscle weakness
• Difficulty speaking or swallowing
• Loss of balance with frequent falls
• Muscle cramps that interfere with daily activities

Your doctor might refer you to a neurologist who specializes in nervous system disorders. Before your appointment, keep a symptom journal noting when problems occur and what makes them better or worse.

Causes

The exact cause of primary lateral sclerosis (PLS) remains unclear, but researchers have identified several biological and genetic factors that may contribute to its development.

In about 5% of cases, a mutation in the SPG7 gene has been found. This gene helps produce paraplegin, a protein involved in mitochondrial function.

While most cases occur sporadically (without family history), this mutation suggests a potential genetic link in rare forms.

PLS involves the gradual degeneration of upper motor neurons, especially in the primary motor cortex. These neurons control voluntary movement. As they deteriorate, communication between the brain and muscles becomes impaired, leading to symptoms such as stiffness and slowed movement.

Although these are not proven causes, researchers believe the following may contribute to disease onset:

• Abnormal protein processing
• Inflammation in the nervous system
• Oxidative stress
• Environmental exposures

Age is also a significant factor. Most people diagnosed with PLS are between 40 and 60 years old when symptoms first appear.

Complications

Primary lateral sclerosis (PLS) often leads to several challenges that affect daily functioning. People with PLS typically experience increasing difficulty with balance and movement as the disease progresses.

Falls become more common due to muscle stiffness and weakness, potentially causing injuries.

Speech problems represent another significant complication. Many patients develop dysarthria, making their speech slow, slurred, or difficult to understand. This communication barrier may lead to frustration and social isolation.

Swallowing difficulties (dysphagia) frequently occur as muscle control deteriorates. This raises risks of choking, poor nutrition, and aspiration pneumonia when food or liquids enter the lungs instead of the stomach.

Daily activities become increasingly challenging. Tasks like dressing, bathing, and eating often require adaptive equipment or assistance from caregivers. Most patients eventually need mobility aids such as canes, walkers, or wheelchairs.

Emotional and psychological impacts include:

• Depression
• Anxiety
• Adjustment difficulties
• Grief over lost abilities

Although it shares some symptoms with other neurological diseases, such as ALS, PLS typically progresses more slowly and has a distinct clinical course.