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Primary Lateral Sclerosis

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Synonyms of Primary Lateral Sclerosis

Disorder Subdivisions

General Discussion

Primary lateral sclerosis (PLS) is a rare, neuromuscular disorder that affects the central motor neurons and is characterized by painless but progressive weakness and stiffness of the muscles of the legs. Such weakness may progress to affect the arms and the muscles at the base of the brain (bulbar muscles). Less frequently, the muscles of the face are affected. In most cases, the disorder affects adults during midlife. The exact cause of primary lateral sclerosis is unknown.


Primary lateral sclerosis is a rare disorder affecting the nerve cells that control voluntary muscles. In most cases, the muscles of the legs are involved first. However, in some cases, the disorder may begin in the muscles of the hands or tongue.

In many cases, the initial symptom of primary lateral sclerosis is progressive muscle weakness and stiffness of the voluntary muscles of legs. The disorder usually affects one leg and then progresses to the other. Affected individuals experience involuntary muscle spasms (spasticity) that result in slow, stiff movements of the legs. As a result, affected individuals may have difficulty walking and maintaining balance, may experience cramping of affected muscles, and may appear clumsy. As the disorder progresses, affected individuals may have increasing difficulties walking and may eventually require a cane or similar device to assist in walking.

Although primary lateral sclerosis begins in the legs, it progresses to affect the muscles of the hands and at the base of the brain. As a result, affected individuals may also exhibit difficulty forming words (dysarthria) and difficulty swallowing (dysphagia). In some cases, these symptoms may precede the development of muscle weakness in the legs. Some affected individuals may experience loss of bladder control late in the course of primary lateral sclerosis.

The specific course of primary lateral sclerosis varies from case to case. The disorder may progress rapidly within a few years or slowly over a few decades.


The exact cause of primary lateral sclerosis is not known. Most cases seem to occur randomly, for no apparent reason (sporadically). Primary lateral sclerosis is one of a group of disorders known as motor neuron diseases. Motor neuron diseases are characterized by malfunction of the nerve cells (motor neurons) within the brain and spinal cord that carry instructions from the brain to the muscles.

Affected Populations

Primary lateral sclerosis is a rare disorder that affects males and females in equal numbers. In most cases, the disorder occurs during the fifth decade. However, according to the medical literature a familial form may exist that affects children. The exact prevalence of primary lateral sclerosis and motor neuron diseases is unknown.

Related Disorders

Symptoms of the following disorders can be similar to those of primary lateral sclerosis. Comparisons may be useful for a differential diagnosis:

Amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease) is a disorder that affects the motor neuron cells. It generally affects both the upper and lower motor neurons and results in the progressive wasting and weakening of those muscles that have lost their nerve supply. A number of different forms of ALS exist, all exhibiting some of the classic symptoms. The early symptoms of ALS include slight muscle weakness, clumsy hand movements, and/or difficulty performing tasks that require delicate movements of the fingers and/or hands. Muscular weakness in the legs may cause tripping and falling. People with ALS may have difficulty swallowing (dysphagia), and speech may be slowed. The exact cause of amyotrophic lateral sclerosis is unknown. (For more information on this disorder, choose "ALS" as your search term in the Rare Disease Database.)

Hereditary spastic paraplegia (HSP) is a group of inherited neurological disorders characterized by progressive weakness (paraplegia) and increased muscle tone and stiffness (spasticity) of leg muscles. HSP is also sometimes referred to as familial spastic paraplegia (FSP) or Strumpell-Lorraine syndrome. The age at symptom onset and the degree of muscle weakness and spasticity may be extremely variable from case to case, including among individuals within the same family (kindred). According to reports in the medical literature, symptom onset may occur as early as infancy or as late as the eighth or ninth decade of life; however, symptoms most often develop during early to mid-adulthood. Initial findings typically include stiffness and relatively mild weakness of leg muscles, balance difficulties, unexplained tripping and falls, and an unusually "clumsy" manner of walking (gait). As the disorder progresses, walking may become increasingly difficult; however, complete loss of the ability to walk is relatively rare. (For more information on this disorder, choose "hereditary spastic paraplegia" as your search term in the Rare Disease Database.)

Multiple sclerosis is a chronic disorder of the central nervous system (CNS) that causes the destruction of the covering (myelin sheath) over the nerves. The course of this disease is variable; it may advance, relapse, remit, or stabilize. The demyelinating plaques or patches scattered throughout the central nervous system interfere with the ability of the nerves to communicate (neurotransmission) and can cause a wide range of neurological symptoms including impairment of speech, numbness or tingling sensation in the limbs and difficulty walking. Dysfunction of the bladder and bowel may also be present. (For more information on this disorder, choose "multiple sclerosis" as your search term in the Rare Disease Database.)

Standard Therapies

Treatment of primary lateral sclerosis involves the use of drugs to help control specific symptoms. Baclofen and tizanidine may be prescribed for spasticity, quinine for cramps, and diazepam, a drug that relaxes muscles, for muscular contractions. Additional treatments may include physical therapy to prevent stiffness of joints, and speech therapy may be needed to aid affected individuals whose ability to speak has been impaired by muscle weakness. Other treatment is symptomatic and supportive.

Investigational Therapies

In the Neuromuscular Disorders Program at Northwestern University Medical School, a study of the cause(s) of sporadic (non-inherited) diseases of the motor neurons, such as primary lateral sclerosis, is in progress. The research team hopes to determine whether genetic factors may predispose an individual to a disease such as PLS and whether sporadic motor-neuron diseases may be the result of not one but several genetic factors.

Blood samples from patients and their living parents, brothers, and sisters are needed for this study. Two tablespoons of blood are needed from each participant. The research team will supply tubes and instructions. Samples may be drawn near the patient’s home.

For information, contact:

Nailah Siddique, RN, MSN, Clinical Nurse Specialist
(312) 503-2712

Scientists are conducting extensive ongoing research on motor neuron diseases in the areas of nerve growth factors, axonal transport, androgen receptor in motor neurons, and DNA/RNA changes.

A clinical trial is underway to study whether the part of the brain that controls movement (motor cortex) works properly in individuals with primary lateral sclerosis. For more information, contact:

National Institute of Neurological Disorders and Stroke (NINDS)
9000 Rockville Pike
Bethesda, Maryland 20892
Patient Recruitment and Public Liaison Office
Phone: 1-800-411-1222
Email: prpl@mail.cc.nih.gov
Website: http://clinicalstudies.info.nih.gov/detail/A_2004-N-0017.html
TTY: 1-866-411-1010

Information on current clinical trials is also posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: prpl@cc.nih.gov

For information about clinical trials sponsored by private sources, contact:

Primary Lateral Sclerosis Resources

NORD Member Organizations:

(To become a member of NORD, an organization must meet established criteria and be approved by the NORD Board of Directors. If you're interested in becoming a member, please contact Susan Olivo, Membership Manager, at solivo@rarediseases.org.)

Other Organizations:


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eMedicine-Primary Lateral Sclerosis: Article by Carmel Armon, MD, MHS


Report last updated: 2007/08/17 00:00:00 GMT+0