electromyography


Also found in: Dictionary, Thesaurus, Encyclopedia, Wikipedia.
Related to electromyography: Electrooculography

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.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.

electromyography

 [e-lek″tro-mi-og´rah-fe]
the recording and study of the intrinsic electrical properties of skeletal muscle. adj., adj electromyograph´ic. When it is at rest, normal muscle is electrically silent, but when the muscle is active, an electrical current is generated. In electromyography the electrical impulses are picked up by needle electrodes inserted into the muscle and amplified on an oscilloscope screen in the form of wavelike tracings. The visual recording may be accompanied by auditory monitoring in which the sounds are amplified.ƒ

Electromyography is useful in diagnosing disorders of the nerves supplying the muscle (as in amyotrophic lateral sclerosis and poliomyelitis) and in disorders affecting the muscle tissues. Recordings usually are obtained while the muscle is relaxed, during voluntary contraction, and during muscle activity that is produced by nerve stimulation. In this way it is possible to determine the presence of a disorder, localize the site, and identify the specific disease producing muscle weakness.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

e·lec·tro·my·og·ra·phy

(ē-lek'trō-mī-og'ră-fē),
1. The recording of electrical activity generated in muscle for diagnostic purposes; both surface and needle recording electrodes can be used, although characteristically the latter is employed, so that the procedure is also called needle electrode examination.
2. Umbrella term for the entire electrodiagnostic study performed in the EMG laboratory, including not only the needle electrode examination, but also the nerve conduction studies.
[electro- + G. mys, muscle, + graphō, to write]
Farlex Partner Medical Dictionary © Farlex 2012

electromyography

EMG Neurology A technique that measures minute electrical discharges produced in skeletal muscle, at rest and during voluntary contraction; EMG is used to diagnose neuromuscular disease; the electrode for EMG is inserted percutaneously and the resulting electrical discharge or motor unit potential is recorded
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.

e·lec·tro·my·og·ra·phy

(EMG) (ĕ-lek'trō-mī-og'ră-fē)
1. The recording of electrical activity generated in muscle for diagnostic purposes; both surface and needle recording electrodes can be used; the latter are more common.
2. Umbrella term for the entire electrodiagnostic study performed in the EMG laboratory, including not only the needle electrode examination, but also nerve conduction studies.
[electro- + G. mys, muscle, + graphō, to write]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012

electromyography

A diagnostic method in which the electrical events associated with muscle contraction are amplified and recorded for analysis. The signals may be picked up by surface electrodes or a needle consisting of two insulated, coaxial conductors may be pushed into the muscle. The method allows distinction to be made between various nerve disorders, disorders affecting the junction between the nerve and the muscle and various muscle disorders.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005

e·lec·tro·my·og·ra·phy

(EMG) (ĕ-lek'trō-mī-og'ră-fē)
1. Recording of electrical activity generated in muscle for diagnostic purposes.
2. Umbrella term for the entire electrodiagnostic study performed in the EMG laboratory, including not only needle electrode examination, but also nerve conduction studies.
[electro- + G. mys, muscle, + graphō, to write]
Medical Dictionary for the Dental Professions © Farlex 2012
References in periodicals archive ?
Electromyography (recording electrical activity of muscles) biofeedback has been shown to enhance recovery of muscle control in people with incomplete spinal-cord injuries (SCI).
The correlation of biomechanical events of deglutition has been described in the literature and its characteristics associated with electromyography establish the suprahyoid musculature as that which reflects the verification of this functional event.
Scapular and shoulder muscle activity was recorded using surface electromyography (sEMG).
Electromyography of the right ADM, FCU, FDP showed severe reduction in voluntary recruitment with fibrillation potentials and positive sharp waves.
Traditional surface electrodes: In the traditional surface electromyography trials, three wireless electrodes (Delsys Trigno, Delsys Inc., USA) sampling at 2000 Hz were attached (Delsys adhesive interface) to the gluteus maximus, vastus lateralis and biceps femoris of the right leg only.
Keywords: Guillain-barre syndrome (GBS), Acute motor axonal neuropathy (AMAN), Electromyography and nerve conduction studies (EMG/NCS).
Electromyography is an electrical technique for medical applications, to appraise and record the electrical activity created by skeletal muscles fibers.
Background: Single-fiber electromyography (SFEMG) has been suggested as a quantitative method for supporting chronic partial denervation in amyotrophic lateral sclerosis (ALS) by the revised EI Escorial criteria.
Laryngeal electromyography demonstrated 25% decreased recruitment in the right cricothyroid and thyroarytenoid muscles.
Along with the new definition of biofeedback and a preliminary definition of applied psychophysiology, this edition has more on specialized applications like electroencephalographic (EEG) biofeedback/neurofeedback and heart rate variability biofeedback, as well as new chapters on surface electromyography, quantitative EEG, consumer products, cognitive-behavioral therapy, relaxation training, and anxiety disorders, asthma, work-related pain, traumatic brain injury, autism spectrum disorders, and substance use disorders.
He has completed an internship in medicine, a residency and chief residency in neurology, and a clinical fellowship in Neuromuscular Disease and Clinical Neurophysiology (electromyography) at Massachusetts General Hospital.