Primary Lateral Sclerosis

National Organization for Rare Disorders, Inc.

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It is possible that the main title of the report Primary Lateral Sclerosis is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.


  • Central Motor Neuron Disease
  • PLS

Disorder Subdivisions

  • None

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.

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



TTY: 1-866-411-1010

Information on current clinical trials is also posted on the Internet at 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


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



Thoene JG, ed. Physicians' Guide to Rare Diseases. Montvale, NJ: Dowden Publishing Company Inc; 1995:367.

Fauci AS, et al., eds. Harrison's Principles of Internal Medicine, 14th Ed. New York, NY: McGraw-Hill, Inc; 1998:2371.

Adams, RD, et al., eds. Principles of Neurology. 6th ed. New York, NY: McGraw-Hill, Companies; 1997:1091-4.

Bennett JC, Plum F, eds. Cecil Textbook of Medicine. 20th ed. Philadelphia, PA: W.B. Saunders Co; 1996:2054.

Berkow R, ed. The Merck Manual-Home Edition. Whitehouse Station, NJ: Merck Research Laboratories; 1997:332.


Swash M, et al. What is primary lateral sclerosis? J Neurol Sci. 1999;170:5-10.

Rowland LP. Primary lateral sclerosis: disease, syndrome, both or neither? J Neurol Sci. 1999;170:1-4.

Rowland LP. Paraneoplastic primary lateral sclerosis and amyotrophic lateral sclerosis. Ann Neurol. 1997;41:703-05.

Reyes-Iglesias Y, et al. Primary lateral sclerosis: a distinct clinical entity in patients with chronic spastic paraparesis. Bol Asoc Med P R. 1990;82:340-42.


Le Forestier N, et al. Primary lateral sclerosis: further classification. J Neurol Sci. 2001;185:95-100.

Le Forestier N, et al. [What's new in primary lateral sclerosis?] Rev Neurol (Paris). 2000;156:364-71.

Peretti-Viton P, et al. MRI of the intracranial corticospinal tracts in amyotrophic and primary lateral sclerosis. Neuroradiology. 1999;41:744-49.

Desai J, et al. IgM paraproteinemia in a patient with primary lateral sclerosis. Neuromuscul Disord. 1999;9:38-40.

Gascon GG, et al. Familial childhood primary lateral sclerosis with associated gaze paresis. Neuropediatrics. 1995;26:313-19.

Caselli RJ, et al. Primary lateral sclerosis: a neuropsychological study. Neurology. 1995;45:2005-09.

Hudson AJ, et al. Clinicopathological features of primary lateral sclerosis are different from amyotrophic lateral sclerosis. Brain Res Bull. 1993;30:359-64.

Pringle CE, et al. Primary lateral sclerosis. Clinical features, neuropathology and diagnostic criteria. Brain. 1992;115 (Pt 2):495-520.

Brown WF, et al. Motor-evoked responses in primary lateral sclerosis. Muscle Nerve. 1992;15:626-29.

Grunnet ML, et al. Primary lateral sclerosis. Neurology. 1989;39:1530-2.

Younger DS, et al. Primary lateral sclerosis. A clinical diagnosis reemerges. Arch Neurol. 1988;45:1304-07.


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



Amyotrophic Lateral Sclerosis Association

27001 Agoura Road

Suite 250

Calabasas Hills, CA 91301-5104


Tel: (818)880-9007

Fax: (818)880-9006

Tel: (800)782-4747

TDD: (818)593-3540



Motor Neurone Disease Association

PO Box 246

Northampton, NN1 2BG

United Kingdom

Tel: 01604250505

Fax: 441604624726



NIH/National Institute of Neurological Disorders and Stroke

P.O. Box 5801

Bethesda, MD 20824

Tel: (301)496-5751

Fax: (301)402-2186

Tel: (800)352-9424

TDD: (301)468-5981


Les Turner Amyotrophic Lateral Sclerosis Foundation, Ltd.

5550 W. Touhy Avenue,

Suite 302

Skokie, IL 60077-3254

Tel: (847)679-3311

Fax: (847)679-9109

Tel: (888)257-1107



Spastic Paraplegia Foundation

5305 Miramar Ln

Colleyville, TX 76034


Tel: (877)773-4483



International Alliance of ALS/MND Associations

P.O. Box 246

Northampton, NN1 2PR

United Kingdom

Tel: 441604611821

Fax: 441604624726



Genetic and Rare Diseases (GARD) Information Center

PO Box 8126

Gaithersburg, MD 20898-8126

Tel: (301)251-4925

Fax: (301)251-4911

Tel: (888)205-2311

TDD: (888)205-3223


For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders, Inc.® (NORD). Cigna members can access the complete report by logging into For non-Cigna members, a copy of the complete report can be obtained for a small fee by visiting the NORD website. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational treatments (if available), and references from medical literature. For a full-text version of this topic, see