Electromyography (EMG) is a test to measure muscle response or electrical activity when a nerve in the muscle is stimulated. The EMG test is a diagnostic tool that helps a neurologist detect neuromuscular abnormalities.
Reasons for an EMG test
An EMG test may be used to help identify the cause of certain symptoms such as muscle weakness, stiffness, spasticity, atrophy, and deformity. An EMG procedure can determine whether a patient is experiencing real muscle weakness as opposed to weakness caused by pain or psychological reasons.
An EMG test is typically used to evaluate conditions and disorders that include:
Motor problems, such as involuntary muscle twitching
Nerve root injury, such as sciatica
Muscle degeneration, such as muscular dystrophy
Neuromuscular diseases, such as myasthenia gravis
Nerve compression or injury, such as carpal tunnel syndrome
Doctors may use the EMG test in concert with a nerve conduction velocity test to differentiate nerve disorders from muscle disorders.
How an EMG test is performed
During an EMG test, small needles are inserted into the muscle through the skin. Electrodes in the needles detect electrical activity in the muscle and display the results on an oscilloscope, a monitor that shows electrical activity in the form of waves. The oscilloscope may include an audio amplifier so that electrical activity can be heard as well.
During the EMG test, patients are typically asked to contract the muscle being tested, for example, by lifting or bending the arm. As the patient contracts the muscle more forcefully, more muscle fibers are activated and the oscilloscope should show stronger electrical activity.
While a healthy muscle shows electrical activity during contraction and not during rest, a damaged muscle or a muscle that has lost input from nerves may show electrical activity during rest, or abnormal electrical patterns during contraction.
An EMG test at Brigham and Women's
As part of the Department of Neurology at Brigham and Women's Hospital (BWH), the Division of Neuromuscular Disease and Electromyography offers comprehensive diagnostic evaluation, consultation and management of all neuromuscular disorders. Serving patient communities locally, nationally and around the world, our staff strives to provide patient-focused, world-class medical care while developing new treatments and cures for neurologic diseases.
We provide diagnostic testing and treatment for a full spectrum of diseases and disorders of the personal nervous system, including: