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Amyotrophic Lateral Sclerosis (ALS) and Other Motor Neuron Diseases (MNDs)

(Lou Gehrig Disease; Lou Gehrig's Disease; Muscle Stimulation Disorders)

By Michael Rubin, MDCM, Professor of Clinical Neurology;Attending Neurologist and Director, Neuromuscular Service and EMG Laboratory, Weill Cornell Medical College;New York Presbyterian Hospital-Cornell Medical Center

Motor neuron diseases are characterized by progressive deterioration of the nerve cells that initiate muscle movement. As a result, the muscles stimulated by these nerves also deteriorate and can no longer function normally.

  • Amyotrophic lateral sclerosis (Lou Gehrig disease) is the most common form of motor neuron disease.

  • Typically, muscles are weak and waste away, and movements become stiff, clumsy, and awkward.

  • Doctors base the diagnosis mostly on results of the evaluation and do electromyography, nerve conduction studies, magnetic resonance imaging, and blood tests to help confirm the diagnosis.

  • There is no specific treatment or cure, but drugs can help lessen symptoms.

For normal muscle function, muscle tissue and nerve connections between the brain and muscle must be normal. Muscle movement is initiated by nerve cells that are located in the spinal cord and in the front part of the brain (called the motor cortex). These nerve cells connect with nerves that stimulate muscles to move (called motor nerves). In motor neuron diseases, these nerve cells progressively deteriorate. As a result, muscles weaken, waste away (atrophy), and can become completely paralyzed even though the muscles themselves are not the cause of the problem.

Using the Brain to Move a Muscle

Moving a muscle usually involves communication between the muscle and the brain through nerves. The impetus to move a muscle may originate with the senses. For example, special nerve endings in the skin (sensory receptors) enable people to sense pain, as when they step on a sharp rock, or to sense temperature, as when they pick up a very hot cup of coffee. This information is sent to the brain, and the brain may send a message to the muscle about how to respond. This type of exchange involves two complex nerve pathways:

  • The sensory nerve pathway to the brain

  • The motor nerve pathway to the muscle

  • If sensory receptors in the skin detect pain or a change in temperature, they transmit an impulse (signal), which ultimately reaches the brain.

  • The impulse travels along a sensory nerve to the spinal cord.

  • The impulse crosses a synapse (the junction between two nerve cells) between the sensory nerve and a nerve cell in the spinal cord.

  • The impulse crosses from the nerve cell in the spinal cord to the opposite side of the spinal cord.

  • The impulse is sent up the spinal cord and through the brain stem to the thalamus, which is a processing center for sensory information, located deep in the brain.

  • The impulse crosses a synapse in the thalamus to nerve fibers that carry the impulse to the sensory cortex of the cerebrum (the area that receives and interprets information from sensory receptors).

  • The sensory cortex perceives the impulse. A person may then decide to initiate movement, which triggers the motor cortex (the area that plans, controls, and executes voluntary movements) to generate an impulse.

  • The nerve carrying the impulse crosses to the opposite side at the base of the brain.

  • The impulse is sent down the spinal cord.

  • The impulse crosses a synapse between the nerve fibers in the spinal cord and a motor nerve, which is located in the spinal cord.

  • The impulse travels out of the spinal cord along the length of the motor nerve.

  • At the neuromuscular junction (where nerves connect to muscles), the impulse crosses from the motor nerve to receptors on the motor end plate of the muscle, where the impulse stimulates the muscle to move.

Motor neuron diseases have various forms, such as the following:

Motor neuron diseases are more common among men and usually develop in people who are in their 50s. The cause is usually unknown. About 5 to 7% of people who have a motor neuron disease have a hereditary type and thus have family members who also have the disease.

Different parts of the nervous system may be affected first. For example, some forms of motor neuron disease affect the mouth and throat first. Others affect a hand or foot first or affect them most severely.

Long-lasting paralysis can lead to permanent shortening of muscles (contractures).

Symptoms

Muscle strength is affected, but people do not have pain or any changes in sensation. Depression is common.

Amyotrophic lateral sclerosis (Lou Gehrig disease)

This progressive form begins with weakness, often in the hands and less frequently in the feet or mouth and throat. Weakness may progress more on one side of the body than on the other and usually proceeds up the arm or leg. Muscles, usually those in the hands and feet, start to waste away (atrophy). Muscle cramps are also common and may occur before the weakness, but no changes in sensation occur. People may lose weight and feel unusually tired.

Over time, weakness increases.

Muscles twitch (called fasciculations). Muscle tone typically increases, and muscles tend to become stiff and tight, leading to muscle spasms (called spasticity). Movements are stiff and clumsy. In some people, muscle tone decreases, making the limbs seem loose and floppy.

Controlling facial expressions may become difficult. Weakening of muscles in the throat may lead to slurred speech and difficulty swallowing (dysphagia). Because swallowing is difficult, people sometimes drool and are more likely to choke on liquids. Food or saliva can be inhaled (aspirated) into the lungs, increasing the risk of pneumonia (called aspiration pneumonia). The voice usually sounds nasal but may be hoarse.

As symptoms progress, people may be unable to control emotional responses and may laugh or cry inappropriately.

Eventually, the muscles involved in breathing weaken, leading to breathing problems. Some people need a ventilator to breathe.

How rapidly amyotrophic lateral sclerosis progresses varies:

  • About 50% of people with the disorder die within 3 years of the first symptoms.

  • About 20% live 5 years.

  • About 10% live 10 years or more.

  • A few people survive as long as 30 years.

Primary lateral sclerosis and progressive pseudobulbar palsy

These forms are rare, slowly progressive variants of amyotrophic lateral sclerosis. Primary lateral sclerosis affects mainly the arms and legs, and progressive pseudobulbar palsy affects mainly the muscles of the face, jaw, and throat. In both disorders, muscles are weak and very stiff and tight (spastic). Muscles twitch (called fasciculations) and waste away.

Emotions may be changeable: People with progressive pseudobulbar palsy may switch from happiness to sadness quickly and without reason. Inappropriate emotional outbursts are common.

Symptoms usually progress for several years before total disability results.

Progressive muscular atrophy

Progressive muscular atrophy can develop at any age. It is similar to amyotrophic lateral sclerosis, but it progresses more slowly, spasticity does not occur, and muscle weakness is less severe. Involuntary contractions or twitching of muscle fibers may be the earliest symptoms.

The hands are usually affected first, followed by the arms, shoulders, and legs. Eventually, the whole body is affected.

Many people with this form survive 25 years or longer.

Progressive bulbar palsy

In progressive bulbar palsy, the nerves controlling the muscles of chewing, swallowing, and talking are affected, making these functions increasingly difficult. The voice may have a nasal tone. In some people, emotions are changeable.

Because swallowing is difficult, food or saliva is often inhaled into the lungs, causing choking or gagging and increasing the risk of pneumonia.

Death, which is often due to pneumonia, usually occurs 1 to 3 years after symptoms appear.

Postpolio syndrome

Some people who have had polio develop postpolio syndrome decades after they have recovered from polio. Postpolio syndrome is more likely to develop in older people and in people who had a severe initial case of polio.

Muscles, usually those that were affected by polio, may become tired, painful, and weak and may waste away. However, in most people who have had polio, such symptoms are not due to postpolio syndrome but to the development of a new disorder, such as diabetes, a ruptured (herniated) disk, or osteoarthritis, or to age-related loss of certain nerve cells in areas where polio had already reduced the number of these nerve cells.

Postpolio syndrome is sometimes considered a motor neuron disease but is sometimes considered a separate disorder.

Diagnosis

  • A doctor's evaluation

  • Tests such as magnetic resonance imaging, electromyography, and nerve conduction studies

Doctors suspect motor neuron disease in adults who have progressive muscle weakness without pain or loss of sensation. Doctors ask people the following:

  • Which parts of the body are affected

  • When symptoms started

  • Which symptoms appeared first

  • How the symptoms have changed over time

This information gives them clues about the cause of symptoms.

Muscle weakness can have many causes. Diagnostic tests, such as the following, are done to help narrow the possibilities:

  • Magnetic resonance imaging (MRI) of the brain and sometimes the spinal cord is done to check for abnormalities that may cause similar symptoms.

  • Electromyography, which involves stimulating muscles and recording their electrical activity, can help determine whether the problem is in nerves or muscles.

  • Nerve conduction studies, which measure how fast nerves transmit impulses, may also be done. The speed of impulses is not affected until late in motor neuron disease, so if impulses are unexpectedly slow, the cause of symptoms may be another disorder.

  • Tests are done to check for other disorders that can cause weakness.

To test for other disorders, doctors may do the following:

  • Blood tests to check for infections and metabolic disorders

  • Urine tests to check for heavy metals (such as lead or mercury) if people have been exposed to them

  • A spinal tap (lumbar puncture) to check for inflammation

  • Genetic tests to check for hereditary disorders such as hereditary neuropathies

Over time, motor neuron diseases tend to cause symptoms that are so characteristic that the diagnosis is obvious without any testing.

Treatment

  • Physical therapy

  • Drugs to relieve symptoms

Motor neuron diseases have no specific treatment or cure. However, researchers continue to look for safe, effective treatments.

Care provided by a team of several types of health care practitioners (a multidisciplinary team) helps people cope with progressive disability. Physical therapy helps people maintain muscle strength and keep joints flexible and thus helps prevent contractures. Nurses or other caregivers must feed people with swallowing difficulties carefully to prevent choking. Some people must be fed through a tube inserted through the abdominal wall into the stomach (gastrostomy tube).

Certain drugs can help relieve symptoms:

  • Baclofen may help make muscles less spastic.

  • Phenytoin or quinine may help decrease cramps.

  • Drugs with anticholinergic effects, such as amitriptyline (an antidepressant), may be used to reduce drooling because one anticholinergic effect is to reduce saliva formation.

  • Amitriptyline or fluvoxamine (also an antidepressant) may help people who have changeable emotions or depression. A drug that combines dextromethorphan (a cough suppressant) with quinidine (used to treat malaria) may help control changeable emotions.

In some people with amyotrophic lateral sclerosis, riluzole, a drug that protects nerve cells, can prolong life for a few months. It is taken by mouth. Edaravone, a new drug, may slow the decline in function to some degree in people with amyotrophic lateral sclerosis.

If pain develops as the disease progresses (for example, if pain occurs when a person has to sit in one position too long), opioids and benzodiazepines, which are mild sedatives, may be used.

In a few people with progressive bulbar palsy, surgery to improve swallowing helps.

Because amyotrophic lateral sclerosis and progressive bulbar palsy are progressive and incurable, people who have one of these diseases are advised to establish advanced directives that specify what kind of care they want at the end of life.

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