Primary Lateral Sclerosis

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Primary lateral sclerosis


Primary lateral sclerosis (PLS) is a rare disease that causes progressive weakness in voluntary muscles such as in the legs, hands, and tongue. PLS is one of the diseases, along with amyotrophic lateral sclerosis (or Lou Gehrig's disease), that are grouped together as motor neuron diseases .


Motor neuron diseases like primary lateral sclerosis develop because the nerve cells that normally control the movement of voluntary muscles degenerate and die. The disease is typically detected in middle age, after age 50. The symptoms of the disorder become progressively worse, with muscles typically affected in the following order: legs and feet, main part of the body (the trunk), arms and hands, and face. PLS is not fatal, and people with the disorder can usually maintain mobility with the use of canes or other assistance.


Primary lateral sclerosis predominates in those over 50 years of age, although people in their mid-30s can be affected. PLS is rare in younger people, although one case of a 20-year-old has been reported. It is estimated that only about 500 people in the United States have the disease. Due to its historically rare occurrence, it is not yet possible to know if the disease is more prevalent in males or females. The incidence of PLS is uncertain. ALS is known to affect two to three people per 100,000. Tentative estimates of the occurrence of PLS are on the order of one person in 10 million, which would make it only about 0.5 percent as prevalent as the already rare ALS.

Causes and symptoms

The cause of the disease is the progressive degeneration and death of the nerves (neurons) that control the movement of voluntary muscles. There is no evidence of agenetic basis for the disease. Some other process determines the nerve cell death. PLS affects a part of the neuron called the cell body (or soma). Specifically, it is the cell bodies of upper motor neurons that are affected. Upper motor neurons are located in the brain. Their loss affects the transmission of a signal to other neurons that eventually control the muscle activity. This specificity distinguishes PLS from ALS. ALS, the most common motor neuron disease, affects both the upper neurons and lower motor neurons located in the spinal cord.

PLS is characterized by weakness of voluntary muscles. Typically, the disease is first noticed as a weakening of the legs, hands, or tongue. Other symptoms include difficulty in maintaining balance and clumsiness, sudden muscle spasms, foot dragging, and difficulty in speaking. The neuron death does not affect regions of the brain that control intellect and behavior.

The muscle weakness becomes progressively worse. For some people, this process can stretch over decades. For others, the progression is much faster. While PLS is related to Lou Gehrig's disease, in PLS there is no degeneration of the spinal motor neurons or the wasting away of muscle mass than occurs in ALS.


Diagnosis is based on the observance of the muscle weakness and the progressive worsening of the weakness. The diagnosis can be delayed because the disease is mistaken for ALS.

Treatment team

Treatment of PLS involves the family physician, a neurologist , and others such as physical therapists. The prolonged nature of the disease means that the energy and commitment of the patient and treatment team must be maintained for a long periods of time, usually decades.


The treatment aims to reduce the discomfort and inconvenience of the disease. There is currently no cure for PLS. Medications such as baclofen, diazepam , and gabapentin have shown effectiveness in reducing muscle spasms in many patients with PLS.

Recovery and rehabilitation

As primary lateral sclerosis is a slowly progressive disorder, emphasis is placed upon maintaining maximum function rather than recovery. Physical therapists can assist with stretching and strengthening exercises to help maintain range of motion and decrease muscle fatigue and spasms. Physical therapists are often involved in assessing gait (manner of walking) and balance, and help select the proper type and size of cane or other device to assist with mobility.

Clinical trials

As of April 2004, one clinical trial was recruiting patients in North America. People between the ages of 40 and 75 were sought in the trial, which seeks to relate measurements of voluntary muscle activity to brain activity. The intention is to better understand the areas of the brain that are involved with PLS. Updated information on the trial can be found at the National Institutes for Health web-site on clinical trials at <>. Aside from the clinical trial, research studies are being funded that seek to develop techniques to diagnose, treat, prevent, and hopefully someday to cure motor neuron diseases.


Because PLS can be a slowly progressing disease, the outlook for a normal life span is good. While life can be greatly changed, a person is still usually able to walk, albeit with the assistance of a cane or other device.



Parker J. N., and P. M. Parker. The Official Parent's Sourcebook on Primary Lateral Sclerosis: A Revised and Updated Directory for the Internet Age. San Diego, Icon Health Publications, 2002.


"NINDS Primary Lateral Sclerosis Information Page." National Institute of Neurological Disorders and Stroke. <> (April 12, 2004).


National Institute for Neurological Diseases and Stroke (NINDS). 6001 Executive Boulevard, Bethesda, MD 20892. (301) 496-5751 or (800) 352-9424. <>.

ALS Association (ALSA). 27001 Agoura Road, Suite 150, Calabasas Hills, CA 91301-5104. (818) 880-9007 or (800) 782-4747; Fax: (818) 880-9006. [email protected]. <>.

Primary Lateral Sclerosis Newsletter. 101 Pinta Court, Los Gatos, CA 95032. (408) 356-8227. [email protected].

Brian Douglas Hoyle, PhD