Primary Lateral Sclerosis
Primary lateral sclerosis is part of a group of disorders known as motor neuron diseases. Motor neurons are cells in the brain and spinal cord that play an essential role in voluntary muscle movements. Motor neuron diseases are caused by degeneration of these cells, and result in an inability initiate and control muscle movements.
Primary lateral sclerosis specifically affects the upper motor neurons. These nerve cells are located in the cerebral cortex and send messages to the lower motor neurons in the brainstem and spinal cord. The lower motor neurons then send messages to the muscles to cause muscle contraction.
Primary lateral sclerosis causes progressive weakness in the muscles of the legs initially, and can progress to the arms, hands, and trunk. It may eventually affect the bulbar muscles, which control speaking, swallowing, and chewing. However, unlike the more common neuromuscular disease known as amyotrophic lateral sclerosis (ALS), primary lateral sclerosis is not thought to shorten life expectancy in most cases. It also progresses more slowly than ALS.
How common is primary lateral sclerosis?
PLS has numerous mimics such as ALS, hereditary spastic paraplegia, and other spinal cord disorders. As such, the number of people affected by primary lateral sclerosis is not well documented, but it is considered a rare disease.
Who gets primary lateral sclerosis?
Primary lateral sclerosis can affect anyone. In most cases, the disease is not inherited.
While the disease can present at any age, the onset usually occurs between the ages of 40 and 60. Like other motor neuron diseases, primary lateral sclerosis is more common in men than in women.
How is primary lateral sclerosis diagnosed?
Primary lateral sclerosis cannot be diagnosed with a single test. After reviewing your personal and family medical history, your neurologist will likely perform several tests to rule out conditions with similar symptoms, such as multiple sclerosis. These tests may include:
- Neurological exam
- Blood tests, which can detect other causes of muscle weakness
- Nerve conduction studies and electromyography (EMG) to test the nerves’ ability to send impulses to muscles and to evaluate the electrical activity of the muscles
- Lumbar puncture (spinal tap), which can help identify multiple sclerosis, infections, and other conditions
- Magnetic resonance imaging (MRI) to look for structural abnormalities such as herniated vertebral discs, multiple sclerosis or spinal cord tumors
- Genetic testing to look for inherited causes of spinal cord disorders such as hereditary spastic paraplegia (HSP)
When symptoms begin, PLS may be mistaken for ALS. Your neurologist may monitor your disease course for at least three or four years before giving a diagnosis of PLS.
Symptoms of Primary Lateral Sclerosis
- Balance problems and falls
- Muscle weakness, stiffness, and/or spasticity usually beginning in the legs and progressing to the trunk, arms, and face
- Slowing of movement
- Slurred speech, drooling, and/or hoarseness as facial muscles weaken
Primary lateral sclerosis can also mimic multiple sclerosis and other conditions, so it is important to see a neurologist for an accurate diagnosis.
Treatments for Primary Lateral Sclerosis
There is no known cure for primary lateral sclerosis, but medications and other therapies may ease symptoms and improve your quality of life.
Muscle relaxants such as baclofen (Gablofen, Lioresal), tizanidine (Zanaflex), or clonazepam (Klonopin) can relieve muscle spasms.
Physical therapy and exercise may help slow muscle weakness and preserve joint immobility. As the disease progresses, your doctor may recommend assistive devices such as a cane, walker, or wheelchair. Occupational therapy may help you maintain your independence.
Your doctor may recommend speech therapy if your facial or swallowing muscles become affected.
Request an Appointment with a Primary Lateral Sclerosis Specialist
Call (602) 406-6262
- Reviewed by: Shafeeq Ladha, MD
- Date of last review: January 12, 2020