Electromyography

Definition

Electromyography (EMG) is used to detect, process, and record electrical muscle activity in order to aid in the diagnosis of neuromuscular disease.

Purpose

EMG is performed most often to help diagnose different neuromuscular diseases causing weakness. EMG can determine whether a particular muscle is responding appropriately to stimulation, and whether a muscle remains inactive when not stimulated. Although EMG is a test of the motor system, it may help identify abnormalities of nerves or spinal nerve roots that may be associated with pain or numbness. EMG may also be useful in determining the cause of certain symptoms, including numbness, atrophy, stiffness, fasciculation, cramps, deformity, and spasticity. EMG results can help determine whether symptoms are due to a muscle disease or a neurological disorder, and, when combined with clinical findings, usually allow a confident diagnosis.

EMG can help diagnose many muscle and nerve disorders, including:

• muscular dystrophy
• congenital, mitochondrial, and metabolic myopathies
• myotonias
• compression neuropathies, such as carpal tunnel syndrome
• peripheral neuropathies
• radiculopathies
• nerve lesions
• amyotrophic lateral sclerosis (Lou Gehrig's disease)
• polio
• spinal muscular atrophy
• Guillain-Barré syndrome
• ataxias
• myasthenias

EMG is also used in gait and motion analysis. EMG is performed dynamically (while the patient executes certain movements) to evaluate gait and movement problems. Clinical applications include assessment of patients with cerebral palsy , traumatic brain injury, spinal cord injury , motor neuron lesions, evaluation of athletic injuries, examination of gait abnormalities associated with stroke, and preoperative assessment of patients having corrective orthopedic surgery.

EMG is one of the tests administered during polysomnography studies. EMG is used to measure neuromuscular activity during sleep to aid in the diagnosis of sleep disorders , such as restless legs syndrome.

Precautions

No special precautions are needed for this test. Patients with a history of bleeding disorders should consult with their treating physician before the test. If a muscle biopsy is planned as part of the diagnostic work-up, EMG should not be performed at the same site, as it may affect the microscopic appearance of the muscle.

Description

EMG is performed using an electromyography unit consisting of electrodes and a computer-based recording unit. Electrodes are used to detect electrical activity generated by stimulating the muscles. Muscles are stimulated by signals from nerve cells called motor neurons . This stimulation causes electrical activity in the muscle, which in turn causes contraction. This electrical activity is detected by the EMG electrode and recorded by the electromyography unit computer.

During an EMG test, the electrode is applied or inserted into the muscle to be tested. Surface, needle, and fine-wire electrodes may be used, depending on the type of stimulation required. Needle electrodes may cause some discomfort, similar to that of an injection. Recordings are made while the muscle is at rest, and then during the contraction. The person performing the test may move the limb being tested, and direct the patient to move it with various levels of force. The electrode may be

repositioned for further recording. Other muscles may be tested as well. A typical session lasts from 30–60 minutes.

A slightly different test, the nerve conduction velocity test, is often performed at the same time with the same equipment. In this test, stimulating and recording electrodes are used, and small electrical shocks are applied to measure the ability of the nerve to conduct electrical signals. This test may cause mild tingling and discomfort similar to a mild shock from static electricity. Evoked potentials may also be performed for additional diagnostic information. Nerve conduction velocity and evoked potential testing are especially helpful when pain or sensory complaints are more prominent than weakness.

Preparation

No special preparation is needed. The doctor supervising and interpreting the test should be given information about the symptoms, medical conditions, suspected diagnosis, neuroimaging studies, and other test results.

Aftercare

Minor pain and bleeding may continue for several hours after the test. The muscle may be tender for a day or two. Pain-relieving medications may be prescribed to relieve muscle soreness.

Complications

There are no significant risks to this test, other than those associated with any needle insertion (pain, bleeding, bruising, or infection ).

Results

The end result of an EMG test is an electromyogram, a computer display or printout of EMG waveforms.

KEY TERMS

Fasciculation —Small involuntary muscle contractions visible under the skin.

Motor neurons —Nerve cells that transmit signals from the brain or spinal cord to the muscles.

Motor unit action potentials —Spikes of electrical activity recorded during an EMG that reflect the number of motor units (motor neurons and the muscle fibers they transmit signals to) activated when the patient voluntarily contracts a muscle.

Nerve conduction velocity testing (NCV) —A type of test that uses an electromyography unit to evaluate electrical potentials from peripheral nerves by measuring how long it takes for a nerve impulse to reach a muscle after stimulation with an electrical current.

Polysomnography —A group of studies (that includes EMG) performed while a patient is sleeping to diagnosis sleep disorders.

There should be some brief EMG activity during needle insertion. This activity may be increased in diseases of the nerve and decreased in long-standing muscle disorders where muscle tissue is replaced by fibrous tissue or fat. Muscle tissue normally shows no EMG activity when at rest or when moved passively by the examiner. When the patient actively contracts the muscle, spikes (motor unit action potentials) should appear on the recording screen, reflecting the electrical activity within. As the muscle is contracted more forcefully, more groups of muscle fibers are recruited or activated, causing more EMG activity.

The interpretation of EMG results is not a simple matter, requiring analysis of the onset, duration, amplitude, and other characteristics of the spike patterns.

Electrical activity at rest is abnormal; the particular pattern of firing may indicate denervation (for example, a nerve lesion, radiculopathy, or lower motor neuron degeneration), myotonia, or inflammatory myopathy.

Decreases in the amplitude and duration of spikes are associated with muscle diseases, which also show faster recruitment of other muscle fibers to compensate for weakness. Recruitment is reduced in nerve disorders.

Health care team roles

EMG is performed by clinicians with special training in electroneurodiagnostic medicine. Usually, a neurologist or physiatrist conducts the EMG study. Some physical therapists trained in EMG may also administer the test. A trained electroneurodiagnostic technologist prepares patients for EMG testing, obtains medical histories, maintains equipment, records and calculates test results, and assists with testing.

Resources

PERIODICALS

American Association of Electrodiagnostic Medicine. "Who is Qualified to Practice Electrodiagnostic Medicine?" Position Statement. Muscle Nerve 22, Supplement 8 (May 1999): S263-S265. <http://www.aaem.net/position_statements/Who's_Qualified.htm>.

Haig, Andrew J., Jeffery B. Gelblum, James J. Rechtien, and Andrew J. Gitter. "Technology Review: The Use of Surface EMG in the Diagnosis and Treatment of Nerve and Muscle Disorders." Muscle Nerve 22, Supplement 8 (May 1999): S239-S242.

Rechtien, James J., Jeffery B. Gelblum, Andrew J. Haig, and Andrew J. Gitter. "Technology Review: Dynamic Electromyography in Gait and Motion Analysis." Muscle Nerve 22, Supplement 8 (May 1999): S233-S238.

ORGANIZATIONS

American Academy of Neurology. 1080 Montreal Avenue, St. Paul, MN 55116. (651) 695-1940. <http://www.aan.com>.

American Association of Electrodiagnostic Medicine. 421 First Avenue SW, Suite 300, East Rochester, MN 55902.(507) 288-0100. <http://www.aaem.net>.

American Society of Electroneurodiagnostic Technologists. 204 West 7th Street, Carroll, IA 51401-2317. (712) 792-2978. <http://www.aset.org>.

OTHER

Jabre, Joe F. "Needle Examination." EMG Manual: The Electronic Version. <http://www.teleemg.com/Chapters/printer/jbr100p.htm>.

Jabre, Joe F. "Nerve Conduction Studies." EMG Manual: The Electronic Version. <http://www.teleemg.com/Chapters/printer/jbr010p.htm>.

Jennifer E. Sisk, M.A.

Electromyography

Definition

Electromyography (EMG) is used to detect, process, and record electrical muscle activity in order to aid in the diagnosis of neuromuscular disease.

Purpose

EMG is performed most often to help diagnose different neuromuscular diseases causing weakness. EMG can determine whether a particular muscle is responding appropriately to stimulation, and whether a muscle remains inactive when not stimulated. Although EMG is a test of the motor system, it may help identify abnormalities of nerves or spinal nerve roots that may be associated with pain or numbness. EMG may also be useful in determining the cause of certain symptoms, including numbness, atrophy, stiffness, fasciculation, cramps, deformity, and spasticity. EMG results can help determine whether symptoms are due to a muscle disease or a neurological disorder, and, when combined with clinical findings, usually allow a confident diagnosis.

EMG can help diagnose many muscle and nerve disorders, including:

• muscular dystrophy
• congenital, mitochondrial, and metabolic myopathies
• myotonias
• compression neuropathies, such as carpal tunnel syndrome
• peripheral neuropathies
• radiculopathies
• nerve lesions
• amyotrophic lateral sclerosis (Lou Gehrig's disease)
• polio
• spinal muscular atrophy

• Guillain-Barré syndrome
• ataxias
• myasthenias

EMG is also used in gait and motion analysis. EMG is performed dynamically (while the patient executes certain movements) to evaluate gait and movement problems. Clinical applications include assessment of patients with cerebral palsy, traumatic brain injury, spinal cord injury, and motor neuron lesions; evaluation of athletic injuries; examination of gait abnormalities associated with stroke; and preoperative assessment of patients having corrective orthopedic surgery.

EMG is one of the tests administered during polysomnography studies. EMG is used to measure neuromuscular activity during sleep to aid in the diagnosis of sleep disorders, such as restless legs syndrome.

Precautions

No special precautions are needed for this test. Patients with a history of bleeding disorders should consult with their treating physician before the test. If a muscle biopsy is planned as part of the diagnostic work-up, EMG should not be performed at the same site, as it may affect the microscopic appearance of the muscle.

Description

EMG is performed using an electromyography unit consisting of electrodes and a computer-based recording unit. Electrodes are used to detect electrical activity generated by stimulating the muscles. Muscles are stimulated by signals from nerve cells called motor neurons. This stimulation causes electrical activity in the muscle, which in turn causes contraction. This electrical activity is detected by the EMG electrode and recorded by the electromyography unit computer.

During an EMG test, the electrode is applied or inserted into the muscle to be tested. Surface, needle, and fine-wire electrodes may be used, depending on the type of stimulation required. Needle electrodes may cause some discomfort, similar to that of an injection. Recordings are made while the muscle is at rest, and then during the contraction. The person performing the test may move the limb being tested, and direct the patient to move it with various levels of force. The electrode may be repositioned for further recording. Other muscles may be tested as well. A typical session lasts from 30-60 minutes.

A slightly different test, the nerve conduction velocity test, is often performed at the same time with the same equipment. In this test, stimulating and recording electrodes are used, and small electrical shocks are applied to measure the ability of the nerve to conduct electrical signals. This test may cause mild tingling and discomfort similar to a mild shock from static electricity. Evoked potentials may also be performed for additional diagnostic information. Nerve conduction velocity and evoked potential testing are especially helpful when pain or sensory complaints are more prominent than weakness.

Preparation

No special preparation is needed. The doctor supervising and interpreting the test should be given information about the symptoms, medical conditions, suspected diagnosis, neuroimaging studies, and other test results.

Aftercare

Minor pain and bleeding may continue for several hours after the test. The muscle may be tender for a day or two. Pain-relieving medications may be prescribed to relieve muscle soreness.

Complications

There are no significant risks to this test, other than those associated with any needle insertion (pain, bleeding, bruising, or infection ).

Results

The end result of an EMG test is an electromyogram, a computer display or printout of EMG waveforms. There should be some brief EMG activity during needle insertion. This activity may be increased in diseases of the nerve and decreased in long-standing muscle disorders where muscle tissue is replaced by fibrous tissue or fat. Muscle tissue normally shows no EMG activity when at rest or when moved passively by the examiner. When the patient actively contracts the muscle, spikes (motor unit action potentials) should appear on the recording screen, reflecting the electrical activity within. As the muscle is contracted more forcefully, more groups of muscle fibers are recruited or activated, causing more EMG activity.

The interpretation of EMG results is not a simple matter, requiring analysis of the onset, duration, amplitude, and other characteristics of the spike patterns.

Electrical activity at rest is abnormal; the particular pattern of firing may indicate denervation (for example, a nerve lesion, radiculopathy, or lower motor neuron degeneration), myotonia, or inflammatory myopathy.

Decreases in the amplitude and duration of spikes are associated with muscle diseases, which also show faster recruitment of other muscle fibers to compensate for weakness. Recruitment is reduced in nerve disorders.

Health care team roles

EMG is performed by clinicians with special training in electroneurodiagnostic medicine. Usually, a neurologist or physiatrist conducts the EMG study. Some physical therapists trained in EMG may also administer the test. A trained electroneurodiagnostic technologist prepares patients for EMG testing, obtains medical histories, maintains equipment, records and calculates test results, and assists with testing.

KEY TERMS

Fasciculation— Small involuntary muscle contractions visible under the skin.

Motor neurons— Nerve cells that transmit signals from the brain or spinal cord to the muscles.

Motor unit action potentials— Spikes of electrical activity recorded during an EMG that reflect the number of motor units (motor neurons and the muscle fibers they transmit signals to) activated when the patient voluntarily contracts a muscle.

Nerve conduction velocity testing (NCV)— A type of test that uses an electromyography unit to evaluate electrical potentials from peripheral nerves by measuring how long it takes for a nerve impulse to reach a muscle after stimulation with an electrical current.

Polysomnography— A group of studies (that includes EMG) performed while a patient is sleeping to diagnosis sleep disorders.

Resources

PERIODICALS

American Association of Electrodiagnostic Medicine. "Who is Qualified to Practice Electrodiagnostic Medicine?" Position Statement. Muscle Nerve 22, Supplement 8 (May 1999): S263-S265. 〈http://www.aaem.net/position_statements/Who's_Qualified.htm〉.

Haig, Andrew J., Jeffery B. Gelblum, James J. Rechtien, and Andrew J. Gitter. "Technology Review: The Use of Surface EMG in the Diagnosis and Treatment of Nerve and Muscle Disorders." Muscle Nerve 22, Supplement 8 (May 1999): S239-S242.

Rechtien, James J., Jeffery B. Gelblum, Andrew J. Haig, and Andrew J. Gitter. "Technology Review: Dynamic Electromyography in Gait and Motion Analysis." Muscle Nerve 22, Supplement 8 (May 1999): S233-S238.

ORGANIZATIONS

American Academy of Neurology. 1080 Montreal Avenue, St. Paul, MN 55116. (651) 695-1940. 〈http://www.aan.com〉.

American Association of Electrodiagnostic Medicine. 421 First Avenue SW, Suite 300, East Rochester, MN 55902. (507) 288-0100. 〈http://www.aaem.net〉.

American Society of Electroneurodiagnostic Technologists. 204 West 7th Street, Carroll, IA 51401-2317. (712) 792-2978. 〈http://www.aset.org〉.

OTHER

Jabre, Joe F. "Needle Examination." EMG Manual: The Electronic Version. 〈http://www.teleemg.com/Chapters/printer/jbr100p.htm〉.

Jabre, Joe F. "Nerve Conduction Studies." EMG Manual: The Electronic Version. 〈http://www.teleemg.com/Chapters/printer/jbr010p.htm〉.

Electromyography

Definition

Electromyography (EMG) is an electrical recording of muscle activity that aids in the diagnosis of neuromuscular disease.

Purpose

Muscles are stimulated by signals from nerve cells called motor neurons. This stimulation causes electrical activity in the muscle, which in turn causes contraction. This electrical activity is detected by a needle electrode inserted into the muscle and connected to a recording device. Together, the electrode and recorder are called an electromyography machine. EMG can determine whether a particular muscle is responding appropriately to stimulation, and whether a muscle remains inactive when not stimulated.

EMG is performed most often to help diagnose different diseases causing weakness. Although EMG is a test of the motor system, it may help identify abnormalities of nerves or spinal nerve roots that may be associated with pain or numbness. Other symptoms for which EMG may be useful include numbness, atrophy, stiffness, fasciculation, cramp, deformity, and spasticity. EMG results can help determine whether symptoms are due to a muscle disease or a neurological disorder, and, when combined with clinical findings, usually allow a confident diagnosis.

EMG can help diagnose many muscle and nerve disorders, including:

• muscular dystrophy
• congenital myopathies
• mitochondrial myopathies
• metabolic myopathies
• myotonias
• peripheral neuropathies
• radiculopathies
• nerve lesions
• amyotrophic lateral sclerosis
• polio
• spinal muscular atrophy
• Guillain-Barré syndrome
• ataxias
• myasthenias

Precautions

No special precautions are needed for this test. Patients with a history of bleeding disorder should consult with their treating physician before the test. If a muscle biopsy is planned as part of the diagnostic work-up, EMG should not be performed at the same site, as it may effect the microscopic appearance of the muscle.

Description

During an EMG test, a fine needle is inserted into the muscle to be tested. This may cause some discomfort, similar to that of an injection. Recordings are made while the muscle is at rest, and then during the contraction. The person performing the test may move the limb being tested, and direct the patient to move it with various levels of force. The needle may be repositioned in the same muscle for further recording. Other muscles may be tested as well. A typical session lasts from 30-60 minutes.

A slightly different test, the nerve conduction velocity test, is often performed at the same time with the same equipment. In this test, stimulating and recording electrodes are used, and small electrical shocks are applied to measure the ability of the nerve to conduct electrical signals. This test may cause mild tingling and discomfort similar to a mild shock from static electricity. Evoked potentials may also be performed for additional diagnostic information. Nerve conduction velocity and evoked potential testing are especially helpful when pain or sensory complaints are more prominent than weakness.

Preparation

No special preparation is needed. The doctor supervising and interpreting the test should be given information about the symptoms, medical conditions, suspected diagnosis, neuroimaging studies, and other test results.

Aftercare

Minor pain and bleeding may continue for several hours after the test. The muscle may be tender for a day or two.

Risks

There are no significant risks to this test, other than those associated with any needle insertion (pain, bleeding, bruising, or infection).

Normal results

There should be some brief EMG activity during needle insertion. This activity may be increased in diseases of the nerve and decreased in long-standing muscle disorders where muscle tissue is replaced by fibrous tissue or fat. Muscle tissue normally shows no EMG activity when at rest or when moved passively by the examiner. When the patient actively contracts the muscle, spikes (motor unit action potentials) should appear on the recording screen, reflecting the electrical activity within. As the muscle is contracted more forcefully, more groups of muscle fibers are recruited or activated, causing more EMG activity.

Abnormal results

The interpretation of EMG results is not a simple matter, requiring analysis of the onset, duration, amplitude, and other characteristics of the spike patterns.

Electrical activity at rest is abnormal; the particular pattern of firing may indicate denervation (for example, a nerve lesion, radiculopathy, or lower motor neuron degeneration), myotonia, or inflammatory myopathy.

Decreases in the amplitude and duration of spikes are associated with muscle diseases, which also show faster recruitment of other muscle fibers to compensate for weakness. Recruitment is reduced in nerve disorders.

Resources

OTHER

Falck, B., E. Stalberg, and L. Korpinen. The Expert Electromyographer. 〈http://www.tut.fi/∼korpinen/EMG.htm〉.

KEY TERMS

Motor neurons— Nerve cells that transmit signals from the brain or spinal cord to the muscles.

Motor unit action potentials— Spikes of electrical activity recorded during an EMG that reflect the number of motor units (motor neurons and the muscle fibers they transmit signals to) activated when the patient voluntarily contracts a muscle.

Electromyography

Definition

Electromyography (EMG) is an electrical recording of muscle activity that aids in the diagnosis of neuromuscular disease, which affects muscle and peripheral nerves.

Purpose

Muscles are stimulated by signals from nerve cells called motor neurons. This stimulation causes electrical activity in the muscle, which in turn causes contraction. A needle electrode inserted into the muscle and connected to a recording device detects this electrical activity. Together, the electrode and recorder are called an electromyography machine. EMG can determine whether a particular muscle is responding appropriately to stimulation, and whether a muscle remains inactive when not stimulated.

EMG is performed most often to help diagnose different diseases causing weakness. Although EMG is a test of the motor system, it may help identify abnormalities of nerves or spinal nerve roots that may be associated with pain or numbness. Other symptoms for which EMG may be useful include atrophy, stiffness, fasciculation (muscle twitching), cramp, deformity, and spasticity . EMG results can help determine whether symptoms are due to a muscle disease or a neurological disorder, and, when combined with clinical findings, usually allow a confident diagnosis.

EMG can help diagnose many muscle and nerve disorders, including:

• muscular dystrophy
• congenital myopathies
• mitochondrial myopathies
• metabolic myopathies
• myotonias
• peripheral neuropathies
• radiculopathies
• nerve lesions
• amyotrophic lateral sclerosis
• polio
• spinal muscular atrophy
• Guillain-Barré syndrome ataxias
• myasthenias
• inflammatory myopathies

Precautions

No special precautions are needed for this test. Persons with a history of bleeding disorder should consult with their treating physician before the test. If a muscle biopsy is planned as part of the diagnostic workup, EMG should not be performed at the same site, as it may affect the microscopic appearance of the muscle. Also, persons on blood thinners should relay this information to the physician performing the EMG.

Description

During an EMG test, a fine needle is inserted into the muscle to be tested. This may cause some discomfort, similar to that of an injection. Recordings are made while the muscle is at rest, and then during the contraction. The person performing the test may move the limb being tested, and direct the patient to move it with various levels of force. The needle may be repositioned in the same muscle for further recording. Other muscles may be tested as well. A typical session lasts from 30–60 minutes, with individual muscles usually studied for a period of two to five minutes.

A slightly different test, the "nerve conduction velocity test," is often performed at the same time with the same equipment. In this test, stimulating and recording electrodes are used and small electrical shocks are applied to measure the ability of the nerve to conduct electrical signals. This test may cause mild tingling and discomfort similar to a mild shock from static electricity. Evoked potentials may also be performed for additional diagnostic information. Nerve conduction velocity and evoked potential testing are especially helpful when pain or sensory complaints are more problematic than weakness.

Preparation

No special preparation is needed. The doctor supervising and interpreting the test should be given information about the symptoms, medical conditions, suspected diagnosis, neuroimaging studies, and other test results.

Aftercare

Minor pain and bleeding may continue for several hours after the test. The muscle may be tender for a day or two.

Risks

There are no significant risks to this test, other than those associated with any needle insertion (pain, bleeding, bruising, or infection).

Normal results

There should be some brief EMG activity during needle insertion. This activity may be increased in diseases of the nerve and decreased in long-standing muscle disorders in which muscle tissue is replaced by fibrous tissue or fat. Muscle tissue normally shows no EMG activity when at rest or when moved passively by the examiner. When the patient actively contracts the muscle, spikes (motor unit action potentials) should appear on the recording screen, reflecting the electrical activity within. As the muscle is contracted more forcefully, more groups of muscle fibers are recruited or activated, causing more EMG activity.

The interpretation of EMG results is not a simple matter, requiring analysis of the onset, duration, amplitude, and other characteristics of the spike patterns.

Electrical activity at rest is abnormal; the particular pattern of firing may indicate denervation (for example, a nerve lesion, radiculopathy , or lower motor neuron degeneration), myotonia, or inflammatory myopathy .

Decreases in the amplitude and duration of spikes are associated with muscle diseases, which also show faster recruitment of other muscle fibers to compensate for weakness. Increases in the amplitude and duration of the spikes are typical of nerve diseases in which some degree of rein-nervation (repair by new nerve connections to muscle) has occurred. Recruitment is reduced in nerve disorders.

Resources

BOOKS

Basmajian, J., and C. DeLuca. Muscles Alive: Their Function Revealed by Electromyography, 5th ed. Baltimore: Williams & Wilkins, 1985.

Richard Robinson

electromyogram (EMG) A recording of the electrical activity of muscle fibres. It is obtained by means of electrodes inserted into the muscle, where they detect the action potentials of individual muscle units. The electrical signals are amplified by an apparatus (electromyograph) and displayed on an oscilloscope. Electromyograms are used in experimental muscle physiology and in diagnosing various nerve and muscle disorders.