Primary Lateral Sclerosis vs ALS – What is the Difference?

Primary lateral sclerosis is a neurodegenerative disease that shares many characteristics with amyotrophic lateral sclerosis (ALS), but there are also significant differences between the two.

Neurodegenerative Diseases

Neurodegenerative disease is an umbrella term that describes quite a wide range of different conditions including Alzheimer’s, Parkinson’s and ALS. Many of these diseases share some clinical features but there are also major differences between them.

Primary lateral sclerosis (PLS) is sometimes conflated with ALS, mainly because the two diseases have similar names.

Here we take a closer look at PLS, what it actually means for the individual who is diagnosed with this disease and how it compares to amyotrophic lateral sclerosis.

What is PLS?

Primary lateral sclerosis is a progressive neurodegenerative disease that affects the upper neurons whose cell bodies are found in the brain. It is a characterized by a degeneration that typically starts in middle age and progresses relatively slowly over many years. It is not a disease that is thought to affect life expectancy.

The disease generally affects the legs first and initial symptoms include difficulty with balance and a feeling of weakness in this area of the body. In the majority of cases, onset occurs in people over the age of 50, though there are some rarer cases (potentially when a genetic component is present) where PLS is seen in children.

Differences Between PLS and ALS

Both PLS and ALS affect the body through the degeneration and eventual death of the neurons which transmit signals to and from the brain. Whilst there are similarities between the two, there are also significant differences.

  • PLS affects only the upper neurons that derive from the brain stem whereas ALS affects both the upper and lower neurons and can have a more wide-ranging impact on the individual.
  • PLS progresses slowly and can be more easily managed compared to ALS, which often progresses rapidly following diagnosis.
  • Although it can be disabling, PLS does not cause muscle wasting and is not considered fatal. Almost half of diagnosed cases of ALS, however, end in fatality within three to five years.
  • There doesn’t seem to be the genetic component in PLS in adults as there appears to be with ALS, though this might change as research continues.

The cause of PLS, as with ALS, is unknown. Some researchers believe that both conditions are actually one disease that produce slightly different effects. In fact, those diagnosed initially with PLS may be reclassified as suffering from ALS at a later date.

PLS Life Expectancy

The median life expectancy for someone diagnosed with ALS is between two and five years, reflecting the invasive nature of the disease.

PLS is much more gradual and the median life expectancy is 20 years. It affects males and females equally.

Causes of PLS

The underlying cause of primary lateral sclerosis is still largely unknown. The condition affects the nerve cells in the brain that are responsible for voluntary movement and damage to the neurons causes numerous problems with mobility.

Specialists often make the distinction between adult and juvenile PLS. In juvenile PLS a genetic component has been identified involving the mutation of a gene called ALS2.

Symptoms of PLS

Man with weakness in his legs
Weakness in the legs is a common symptom of PLS

The symptoms of PLS take many years to progress compared to ALS. Common symptoms associated with primary lateral sclerosis include:

  • Spasticity or muscle twitching in the leg accompanied by weakness and stiffness. This usually affects one limb initially and then spreads.
  • The individual with PLS may discover they have difficulty walking and have problems with their balance.
  • Weakness or stiffness will gradually spread from the legs up to the stomach and torso, finally affecting areas like the arms, jaw and facial muscles.
  • In later stages of the disease, individuals can experience difficulty speaking and eating. Breathing may also be impaired.

Treatment for PLS

The slow progression of PLS compared to many cases of ALS means that individuals have much more time to adjust and implement coping measures. Compared to individuals with ALS, those with PLS will have fewer issues to deal with, though coping with a growing disability is still a major challenge.

Diagnosis of PLS is usually through eliminating other potential conditions. As with ALS, there is no current cure for the disease and treatment involves managing the progression through a variety of methods. These may include:

  • Medications to help reduce muscle spasms.
  • Physical therapy to improve muscle tone and mobility.
  • Speech therapy to help maintain facial muscles affected by the disease.

A range of assistive devices can be incorporated to aid the individual including walking sticks and wheelchairs. This is usually arranged in consultation with an occupational therapist and may also include modifications to the home to aid mobility.