Primary lateral sclerosis (PLS) is a type of motor neuron disease that causes nerves within the brain to slowly break down. This makes the nerves unable to activate the motor neurons in the spinal cord, which control muscles. PLS causes weakness in your voluntary muscles, such as those you use to control your legs, arms and tongue.
This condition can develop at any age, but it usually occurs between ages 40 and 60. A subtype of primary lateral sclerosis, known as juvenile primary lateral sclerosis, begins in early childhood and is caused by an abnormal gene passed from parents to children.
Primary lateral sclerosis is often mistaken for another, more common motor neuron disease called amyotrophic lateral sclerosis (ALS). However, primary lateral sclerosis progresses more slowly than ALS, and in most cases isn't fatal.
Signs and symptoms of primary lateral sclerosis (PLS) usually take years to progress. They include:
- Stiffness, weakness and muscle spasms (spasticity) in your legs, often starting in one leg
- Tripping, difficulty with balance and clumsiness as the leg muscles weaken
- Weakness and stiffness progressing to your trunk, then your arms, hands, tongue and jaw
- Hoarseness, as well as slowed, slurred speech and drooling as the facial muscles weaken
- Difficulties with swallowing and occasionally breathing late in the disease
Less commonly, PLS begins in your tongue or hands and then progresses down your spinal cord to your legs.
When to see a doctor
Make an appointment to see your doctor if you have persistent problems with stiffness or weakness in your legs, or with swallowing or speaking.
If your child develops involuntary muscle spasms or seems to be losing balance more often than usual, make an appointment with a pediatrician for an evaluation.
In primary lateral sclerosis (PLS), the nerve cells in the brain that control movement fail over time. This loss causes movement problems, such as slow movements, balance problems and clumsiness.
Adult primary lateral sclerosis
The cause of adult primary lateral sclerosis is unknown. In most cases, it's not an inherited disease, and it's not known why or how it begins.
Juvenile primary lateral sclerosis
Juvenile primary lateral sclerosis is caused by mutations in a gene called ALS2.
Although researchers don't understand how this gene causes the disease, they know that the ALS2 gene gives instructions for creating a protein called alsin, which is present in motor neuron cells.
When the instructions are changed in someone with juvenile PLS, the protein alsin becomes unstable and doesn't work properly, which in turn impairs normal muscle function.
Juvenile primary lateral sclerosis is an autosomal recessive disease, meaning that both parents have to be carriers of the gene to pass it to their child, even though they don't have the disease themselves.
Although the average progression of primary lateral sclerosis (PLS) lasts around 20 years, the disease has highly variable effects from person to person. Some people continue to walk, but others eventually need to use wheelchairs or other assistive devices.
Adult PLS isn't thought to shorten life expectancy, but it can gradually affect the quality of your life as more muscles become disabled. Weaker muscles can cause you to fall, which can result in injuries.
There is no single test that confirms a diagnosis of primary lateral sclerosis (PLS). In fact, because the disease can mimic signs and symptoms of other neurological diseases such as multiple sclerosis and ALS, your doctor is likely to order several tests to rule out other diseases.
After taking a careful record of your medical history and family history and performing a neurological examination, your doctor might order the following tests:
- Bloodwork. Blood tests check for infections or other possible causes of muscle weakness.
MRI. An MRI or other imaging tests of your brain or spine might reveal signs of nerve cell degeneration.
An MRI can show other causes of your symptoms, such as structural abnormalities, multiple sclerosis or spinal cord tumors.
Electromyogram (EMG). During an EMG, your doctor inserts a needle electrode through your skin into various muscles. The test evaluates the electrical activity of your muscles when they contract and when they're at rest.
This test can measure the involvement of lower motor neurons, which can help to differentiate between PLS and ALS.
- Nerve conduction studies. These tests use a low amount of electrical current to measure your nerves' ability to send impulses to muscles in different areas of your body. This test can determine if you have nerve damage.
- Spinal tap (lumbar puncture). Your doctor uses a thin, hollow needle to remove from your spinal canal small samples of the fluid that surrounds your brain and spinal cord (cerebrospinal fluid) for laboratory analysis. A spinal tap can help rule out multiple sclerosis, infections and other conditions.
Sometimes doctors wait three to four years before finalizing a diagnosis because early ALS can look just like PLS until additional symptoms surface a few years later. You might be asked to return for repeat electromyography testing over three to four years before the PLS diagnosis is confirmed.
There are no treatments to prevent, stop or reverse PLS. Treatment, which focus on relieving symptoms and preserving function, include:
Medication. Your doctor might prescribe medication such as baclofen, tizanidine (Zanaflex) or clonazepam (Klonopin) to relieve muscle spasms (spasticity). These medications are taken by mouth.
If your spasticity isn't controlled with oral medication, your doctor might recommend surgically implanting a medication pump to deliver baclofen directly to your spinal fluid (intrathecal baclofen).
If you have depression, your doctor might prescribe antidepressants. Amitriptyline and other drugs also can help drooling problems.
- Physical therapy. Stretching and strengthening exercises can help maintain muscle strength, flexibility and range of motion, and prevent joint immobility. Heating pads can help relieve muscle pain.
- Speech therapy. If your facial muscles are affected by PLS, speech therapy might help.
- Assistive devices. Physical or occupational therapists might evaluate you periodically to determine whether you need assistive devices, such as a cane, walker or wheelchair, as PLS progresses.
Periods of feeling down about having primary lateral sclerosis are expected and normal. Dealing with the reality of an incurable, progressive disease can be challenging. To cope with the disease and its effects, consider these tips:
Seek emotional support. Family and friends can be great sources of comfort and support when you're wrestling with the emotional aspects of long-term disease.
Because PLS is an uncommon diagnosis, it might be a challenge to find a local support group for people with your condition. However, some online discussion groups are available. It might help to see how others cope with the disease.
Get professional help if you need it. When faced with a chronic illness, it's not unusual to become overwhelmed at times. Seek professional counseling for another perspective, or if you're struggling with depression and need advice on treatment.
Know and use resources available to you. If you reach a point where your disease is restricting your activities significantly, ask your doctor about devices designed to help you stay independent.
In addition, there are social services available to people with disabilities of all kinds. Try to learn all you can about the resources available to you. Sometimes relying on your community for help can strengthen ties in new ways.