Primary lateral sclerosis

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at September 22, 2016
StartDiseasesPrimary lateral sclerosis

Primary lateral sclerosis (PLS) is a rare motor neuron disease that causes a progressive degeneration of the nerve cells (neurodegeneration) that control the voluntary muscles. The condition is not usually associated with pain but may eventually result in paralysis. The primary symptoms are stiffness, weakness, and loss of control of one's arms, legs, and tongue.


Definition & Facts

Primary lateral sclerosis is sometimes misdiagnosed as amyotrophic lateral sclerosis (ALS) but is far less deadly. Those who are diagnosed with primary lateral sclerosis live on average twenty years after diagnosis, whereas the survival rate for those diagnosed with ALS is two to five years.

Primary lateral sclerosis can occur at any age but is more commonly found in adults between the ages of 40 and 60. Males and females are equally likely to be affected.

The severity of symptoms varies among individuals. Some may retain the ability to walk, but it is often accompanied by pain and a significantly shortened stride.

Symptoms & Complaints

Symptoms of the condition typically develop slowly, sometimes progressing over 20 years or longer. As muscles weaken, affected individuals may be more likely to fall and receive secondary injuries which could result in death.

The ability to drive, operate machinery, and work in certain fields is often compromised as a result of the condition. Stiffness and weakness in the legs caused by PLS often results in muscle spasms, clumsiness, tripping, and difficulties with balance.

Symptoms usually begin in one leg and progress asymmetrically. They will eventually spread to the trunk of the body and then begin to affect the arms and hands. As the disease progresses, affected individuals may begin to experience hoarseness of the throat. Facial muscles often weaken, resulting in drooling and slowed and slurred speech.

At the end stage of the disease, it is common for patients to experience problems with swallowing (dysphagia) and difficulty breathing. In rare cases, symptoms may begin in the hands or mouth and then spread down to the legs through the spinal cord. Some patients also experience eye movement disorders, urinary problems, and cognitive impairment.


Primary lateral sclerosis has not been associated with a specific cause and usually occurs completely randomly. There is no evidence of a family connection with adult-onset primary lateral sclerosis. A rare subtype of the condition known as juvenile primary lateral sclerosis begins in early childhood and is caused by an inherited abnormality in the ALS2 gene.

Diagnosis & Tests

Primary lateral sclerosis is often misdiagnosed as amyotrophic lateral sclerosis (ALS), or Lou Gehrig’s disease. This is a more common and often fatal motor neuron disease that is associated with similar symptoms. The primary difference is that ALS affects both the upper motor neurons and lower motor neurons while PLS only impacts the upper motor neurons. It may take several years to differentiate between PLS and ALS, and repeated testing over the course of three to four years may be needed before a final diagnosis is given.

The physician will begin with a review of the patient’s medical history and family history and details regarding the onset and severity of symptoms. Physical examinations and neurological examinations will be completed and a complete blood count will be ordered.

There is no specific test for PLS and a series of diagnostic exams are often necessary to rule out other diseases and reach a differential diagnosis. A magnetic resonance imaging (MRI) allows the physician to review the condition of the brain and spine and a positron emission tomography (PET) scan helps to diagnose degenerative brain disease.

Electromyograms (EMG), nerve conduction studies, and evoked potentials all use electrical currents to evaluate nerve, muscle, and brain function. In some cases, a spinal tap or lumbar puncture may be used to withdraw cerebrospinal fluid from the spinal canal for laboratory testing.

Treatment & Therapy

There is no cure for primary lateral sclerosis and treatment is primarily focused on relieving symptoms and preserving muscle function. Early diagnosis and treatment is often the key to avoiding medical complications, retaining the ability to walk, and avoiding secondary injuries from falling. Due to the slow progression of the disease, individuals and families are often able to adapt to the condition and have sufficient time to seek the resources needed to effectively deal with the symptoms as they arise.

In some cases, lifestyle changes such as staying active, eating a healthy and balanced diet, and avoiding obesity can help to reduce the severity of symptoms and improve the quality of life. As muscle weakness progresses, occupational therapy or speech therapy may be needed. Physical therapy can help to keep joints mobile and reduce muscle atrophy.

Assistive devices such as leg braces, a cane, walker, or wheelchair are often needed. In cases where the facial muscles have been impacted, a speech synthesizer may be used to help affected individuals maintain independence. Support groups may help both the affected individual and the family to deal with the impact of the disease.

The first line of medical treatment is usually the use of prescriptions to control muscle spasms. The most commonly used muscle relaxant medications are baclofen, tizanidine or clonazepam. PLS often causes uncontrollable cramping and intense, disabling pain when the muscles are stretched. Cramping can be managed with quinine or phenytoin, and pain medication may also be prescribed. If oral medications fail to control the symptoms, a pump may be surgically implanted to release baclofen directly into the spinal fluid. This is a highly invasive procedure and not all patients will qualify.

Patients suffering from PLS may also struggle with depression and can benefit from antidepressant drugs. When drooling becomes a problem, amitriptyline may be prescribed. Following diagnosis, patients will need ongoing treatment throughout their lifetimes. Treatment at a multidisciplinary clinic may be preferable as patients can be seen by a team of various therapists, physicians, dietitians, and nutritionists in one location. Some patients may qualify for participation in clinical trials aimed at improving treatment options and seeking a cure.

Prevention & Prophylaxis

There are no preventative measures available to avoid adult-onset primary lateral sclerosis. Juvenile PLS has been determined to be caused by an autosomal recessive condition. In order for it to be passed on to a child, both parents must be genetic carriers of the mutated gene. Since two sets of the gene are needed to cause the disease, neither of the carrier parents may have the disease.

If a child is diagnosed with the condition, prospective parent(s) may consider genetic counseling in order to determine the likelihood of passing the condition on to future children.