Primary lateral sclerosis (PLS) is a rare neuro-muscular disease, belonging to a group of disorders known as motor neuron diseases, which leads to progressive weakness in voluntary muscle movement. PLS affects the upper motor neurons (also called corticospinal neurons) in the arms, legs and face. It occurs when nerve cells in the motor regions of the cerebral cortex (the thin layer of cells covering the brain responsible for higher level mental functions) gradually degenerate, causing movements to be slow and labourious. The condition causes weakness in your voluntary muscles, such as those required to control the legs, arms and tongue. The disease can happen at any age, but it usually occurs between ages 40-60 years. 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. PLS 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. 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, however, 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 is responsible for giving 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. Adults who get primary lateral sclerosis don’t appear to have the same gene mutation. 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.
There is no single test that confirms the diagnosis. In fact, because the disease can mimic signs and symptoms of other neurological diseases such as multiple sclerosis and ALS, your doctor may order several tests to rule out other diseases.
After taking a careful record of your medical history, family history and performing a neurological examination, you may have to go through a range of diagnostic exams including blood tests and scans, some to confirm PLS and others to rule out other possible diseases (See Tech & Procedures). After other diseases are ruled out, your doctor may make a preliminary diagnosis of PLS. Sometimes doctors wait three to four years before confirming the diagnosis, because early amyotrophic lateral sclerosis (ALS) can look just like PLS until additional symptoms surface a few years later. You may be asked to return for repeat electromyography testing over three to four years before the PLS diagnosis is confirmed.
The treatments for primary lateral sclerosis (PLS) focus on relieving symptoms and preserving function. Your doctor may prescribe medication to relieve muscle spasms (spasticity). If your spasticity isn’t controlled with oral medication, your doctor may recommend surgically implanting a medication pump to deliver baclofen directly to your spinal fluid (intrathecal baclofen). If you experience depression, your doctor may prescribe antidepressants. Amitriptyline and other drugs also can help drooling problems.
Physical therapy: Stretching and strengthening exercises may help to maintain muscle strength, flexibility, range of motion and to prevent joint immobility. Heating pads can help relieve your symptoms of muscle pain.
Speech therapy: If your facial muscles are affected by PLS, speech therapy can help you compensate for speech and facial muscle problems.
Blood test: Done to check for infections or other possible causes of muscle weakness.
Magnetic resonance imaging (MRI): An MRI or other imaging tests of your brain or spine may reveal signs of nerve cell degeneration.Your doctor also may order an MRI to look for 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.
Nerve conduction studies: These tests use a low amount of electrical current to test and 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): In this procedure, your doctor uses a thin, hollow needle to remove small samples of the cerebro spinal — surrounding the brain and spinal cord — fluid from within your spinal canal for laboratory analysis. A spinal tap can help rule out multiple sclerosis, infections and other conditions.
Positron emission tomography (PET): A PET scan may reveal degenerative changes in the brain and help diagnose PLS.