PLS vs ALS: What Are the Differences?

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Primary lateral sclerosis (PLS) and amyotrophic lateral sclerosis (ALS) are rare neurodegenerative diseases that progressively affect voluntary muscle movement over time. However, there are important differences between the two conditions.

PLS affects only the upper motor neurons, occurs more gradually, and is debilitating but not fatal. ALS affects both upper and lower motor neurons, occurs more rapidly, leads to muscle wasting, and has a more devastating effect than PLS.

This article will explain more about the differences between PLS and ALS, their symptoms, diagnoses, and treatment.

Doctor talking to older man in examination room

FatCamera / Getty Images

Symptoms

Many symptoms of PLS and ALS are very similar and can be confused with the other in earlier stages of the disease process. This is because both diseases lead to the degeneration and death of neurons, which are responsible for transmitting information to and from the brain.

Symptoms of PLS

Symptoms of PLS take several years to progress, while symptoms of ALS come on more rapidly. In addition, those diagnosed with PLS usually go on to live a normal life span, and those diagnosed with ALS typically have a life expectancy of three to five years.

PLS is more common in men than women, and the onset of the disease is typically between ages 40 and 60. PLS progresses gradually over several years or even decades. 

Common symptoms of PLS include:

  • Weakness in the legs
  • Muscle twitching and spasticity
  • Difficulty walking
  • Balance problems
  • Clumsiness
  • Slowing of movement
  • Speech or swallowing problems
  • Stiffness and weakness start in the legs and slowly spread to the torso area

Symptoms of ALS

ALS symptoms typically don't develop until age 50 or later; however, symptoms can start earlier. People with ALS experience a loss of coordination and muscle strength that progressively worsens, eventually affecting more muscle groups.

Symptoms of ALS also eventually get to a point in which routine functions such as swallowing, walking, or standing become impossible.

Other common symptoms of ALS include:

  • Weakness in the arms and legs
  • Weakness in the ability to swallow, which leads to choking easily, gagging, or drooling
  • Difficulty breathing
  • Difficulty walking and climbing stairs
  • Difficulty lifting
  • Speech issues, including slurring or slow speech
  • Head drop from weakened neck muscles
  • Hoarseness in the voice
  • Muscle cramps or stiffness
  • Weight loss

People with ALS retain cognition; however, in rare cases, people may develop dementia, leading to memory loss.

Causes

In most cases, the exact causes of PLS and ALS are unknown and appear to occur randomly.

PLS Causes

PLS is a genetic disease, meaning it's caused by a poorly functioning gene known as gene variant SPG7. People may also inherit PLS from their parents.

ALS Causes

Research suggests that genetics and environment play a role in the development of ALS. More than a dozen genetic mutations are associated with some cases of ALS, including the SOD1 gene.

Environmental factors that may play a role in the development of ALS include:

  • Exposure to toxins or other infectious agents
  • Viruses
  • Physical trauma
  • Poor nutrition

Diagnosis

Several diagnostic tests help diagnose ALS and PLS. No single test can provide a definitive diagnosis for either. Your healthcare provider may likely start by gathering your past medical history, performing a physical examination, and gathering information about symptoms. They may also perform additional diagnostic tests not on the list below to help rule out other medical conditions.

Diagnostic tests for PLS and ALS may include:

  • Clinical examination
  • Neurological examination
  • Blood and urine tests
  • Electromyography (EMG)
  • A nerve conduction study (NCS)
  • Lumbar puncture
  • Magnetic resonance imaging (MRI) of the brain and spine
  • Muscle biopsy
  • Genetic testing
  • Swallowing studies
  • Repeat neurological examinations and diagnostic testing to assess if symptoms are getting worse

Because ALS symptoms develop and worsen so much more quickly than PLS, a diagnosis is easier to make within the first year or two.

Treatment

A proper diagnosis of PLS or ASL is vital because treatments can vary depending on the disease. Unfortunately, no treatments can reverse or cure motor neuron damage caused by PLS or ALS. Treatments can help control symptoms, prevent complications, and improve the quality of life for patients with one of the diseases.

PLS Treatment

Treatment for PLS is typically symptomatic and may include the following:

  • Muscle relaxants to reduce spasticity, which may include Lioresal (baclofen), Zanaflex (tizanidine), or benzodiazepines
  • Pain relieving drugs
  • Antidepressants for depression
  • Physical therapy
  • Occupational therapy and rehabilitation to prevent joint immobility and slow muscle atrophy
  • Assistive devices such as supports or braces
  • Speech synthesizers
  • Wheelchairs if needed
  • Speech therapy if facial muscles are affected

ALS Treatment

Because symptom onset progresses more rapidly and is more debilitating additional supportive health care is essential with various providers, including:

  • Physicians
  • Pharmacists
  • Neurologists
  • Physical, occupational, speech, and respiratory therapists
  • Nutritionists
  • Social workers
  • Clinical psychologists, and
  • Home care and hospice nurses.

A multidisciplinary team approach can help provide an individualized treatment plan to help people stay as mobile, comfortable, and independent as possible.

Medications to help manage ALS symptoms may include:

  • Rilutek (riluzole): an oral medication believed to reduce damage to motor neurons. Research shows that this drug may help increase patient survival by a few months.
  • Radicava (edaravone): an intravenous infusion medication believed to help slow the decline in daily activities

Healthcare providers may also prescribe medications to help with the following:

  • Muscle cramps
  • Muscle stiffness
  • Excess saliva
  • Pain management
  • Depressions
  • Sleep problems
  • Constipation

Additional devices that may help people with ALS include:

  • Computer-based speech synthesizers that use eye-tracking technology to help people with yes and no answers
  • A brain-computer interface (BCI) system that allows ALS patients to communicate or control equipment such as a wheelchair using only brain activity

As ALS progresses, the muscles that help with breathing weaken, and people may need additional breathing support, including:

  • Noninvasive ventilation (NIV): Oxygen is delivered through a mask over the nose and/or mouth.
  • Mechanical ventilation (respirators): A machine inflates and deflates the lungs for the patient.

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Prevention

Unfortunately, there is no clear way to prevent PLS or ALS. However, you may want to consider talking with a genetic counselor if you have a family history of motor neuron diseases.

Summary

Primary lateral sclerosis (PLS) and amyotrophic lateral sclerosis (ALS) are two rare neurodegenerative diseases that progressively affect voluntary muscle movement over time. Although the diseases are similar, they have different symptoms and require different treatments.

Symptoms of PLS take several years to progress, while symptoms of ALS come on more rapidly. In addition, those diagnosed with PLS usually go on to live normal lifespans, and those diagnosed with ALS typically have a life expectancy of three to five years.

A Word From Verywell

Talk to your healthcare provider about your diagnosis and treatment plan if you or a loved one is diagnosed with PLS or ALS. It is essential to see your provider regularly to see if symptoms worsen over time and to ensure you have a correct diagnosis. Neuromotor diseases are difficult to live with but know that there are many treatments and medical experts who can help you manage symptoms.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Sparrow. Primary lateral sclerosis (PLS).

  2. ALS Therapy Institute. ALS and PLS: two similar neurodegenerative diseases with important differences.

  3. National Institute of Neurological Disorders and Stroke. Primary lateral sclerosis.

  4. Medline Plus. Amyotrophic lateral sclerosis (ALS).

  5. National Center for Advancing Translational Sciences. Primary lateral sclerosis.

  6. National Institution of Neurological Disorders and Stroke. Amyotrophic lateral sclerosis (ALS) fact sheet.

  7. National Institution for Rare Disorders. Primary Lateral Sclerosis.

By Sarah Jividen, RN
Sarah Jividen, RN, BSN, is a freelance healthcare journalist and content marketing writer at Health Writing Solutions, LLC. She has over a decade of direct patient care experience working as a registered nurse specializing in neurotrauma, stroke, and the emergency room.