Difference between ALS and PLS (With Table)

ALS and PLS are both diseases prevalent in the modern world that affect the nervous system. It is important to be aware of these diseases and the difference between them.

Both of these diseases take place in people over 40 years of age. However, it is possible to be diagnosed with either of these diseases at any age.


The main difference between ALS (Amyotrophic Lateral Sclerosis) and PLS (Primary Lateral Sclerosis) is that Amyotrophic Lateral Sclerosis affects the upper and lower motor neurons.
On the other hand, Primary Lateral Sclerosis affects only the upper motor neurons alone.

ALS, a type of progressive neuron system disease is known to be a very fatal disease. No cure for Amyotrophic Lateral Sclerosis has been found to date. The cause of a majority of cases of this neuron disease is also unknown.

PLS, also being a progressive neuron system disease is known to be a less fatal version of ALS. Some scholars even argue against PLS being a separate disease and instead say that it is simply a less severe version of ALS, that may even lead to ALS in the future.

Comparison Table Between ALS and PLS

Comparison ParameterAmyotrophic Lateral Sclerosis Primary Lateral Sclerosis
Affected Neurons ALS affects both upper and lower motor neurons.PLS affects the upper motor neurons alone.
Life Expectancy PLS is generally not known to reduce life expectancy.The average life expectancy is about 2-5 years after diagnosis.
CauseThe cause of ALS is not known. Juvenile PLS is caused by mutations in a gene called ALS2.
Occurrence ALS has an incidence rate of about 2 individuals out of 100,000 every year. PLS is known to have an incidence rate of about 1 case every 10 million people per year.
Hereditary Nature Every individual with ALS has a 50% chance of passing on the disease to their offspring. PLS is generally not considered a genetic disease as most cases occur sporadically.

What is ALS?

ALS, short for Amyotrophic Lateral Sclerosis is a progressive nervous system disease. It affects nerve cells in the spinal cord and in the brain which causes an inability of muscle control.

It is often called Lou Gehrig’s disease, after the baseball player who is popularly known to have inherited the disease.

5-10% cases of ALS have been known to be inherited. The cause for the rest is unknown.

ALS generally begins on a smaller scale. It could begin with muscle twitching, slurring of words or weakness in a limb.

It is a fatal disease, known to kill within two to five years of diagnosis. It has no cure.

Symptoms of ALS vary from person to person. Some common symptoms observed are –

  • Difficulty Walking
  • Tripping and Falling
  • Weakness in feet, legs and ankles
  • Hand Weakness or clumsiness
  • Slurred Speech
  • Trouble in swallowing
  • Muscle cramps
  • Inappropriate laughing, crying or yawning
  • Twitching in arms, shoulders and tongue

ALS causes motor neurons to deteriorate and eventually die. When motor neurons are damaged, they fail to send messages between the brain & the spinal cord, and to the muscles throughout the body.
This prevents the muscles from functioning normally.

What is PLS?

Like ALS, PLS is a progressive degenerative disease of the motor neurons.

The progress of PLS is more gradual and less devastating than ALS. Thanks to this, PLS generally does not shorten the life expectancy of its victims.

PLS does not result in muscle wasting. Although it is disabling, it is not fatal. Some ALS specialists also believe that PLS may be a disease on the ALS continuum and may not be a separate disease in itself. Just a slow-progressing type of ALS.

This is also due to the fact that PLS has the potential to be reclassified as ALS if both upper and lower motor neurons start being affected over time.

PLS generally begins with stiffness and pain due to spasticity. Gradually, PLS may develop problems in balance and lower back & neck pains.

As the upper limbs start being affected, daily chores become increasingly difficult. Speech impediments start developing. Swallowing and breathing become compromised in later stages of the disease.

There is no treatment that slows or reverse PLS.
Symptoms can be treated using drugs to reduce pain, muscle cramps and muscle spasticity.
Physical therapy can also be used to combat joint immobility and speech therapy for those whose facial muscles are affected.

The age range for onset of ALS ranges from 35 to 66 years, with the median age being about 50.5 years.

Individuals suffering from PLS are advised to visit neurologists regularly to be tested for characteristic neuronal degeneration of ALS.

Main Differences Between ALS and PLS

  1. ALS affects both the upper and lower motor neurons of the person affected. PLS, being less severe is known to only affect upper motor neurons.
  2. PLS being a less severe disease does not reduce life expectancy. ALS has been known to kill individuals affected about two to five years after diagnosis.
  3. The cause of ALS is not known, with a small minority of cases being hereditary. PLS is caused by mutations in a gene called ALS2.
  4. PLS is a lesser occuring disease than ALS, affecting every 1 person out of 10 million compared to ALS’ 200 out of 10 million.
  5. The chances of a person receiving ALS from a parent suffering from the disease is about 50%. PLS occurs more sporadically.


It is important to increase awareness about these diseases. As the causes of them are basically unknown, they can affect anybody at any time.

Having basic knowledge about certain diseases helps in getting these diseases diagnosed on time. This can also lead to the treatment process being started on time which may prolong the affected person’s life expectancy in more fatal cases.

Being caught off-guard by being affected by such a disease yourself or a family member being affected can be devastating. Having more knowledge about this topic should help you to fight it better.