Electromyogram
(EMG)
Medical Author: William C.
Shiel Jr., MD, FACP, FACR
Medical Editor: Melissa Conrad Stöppler, MD
What is an electromyogram?
An electromyogram (EMG) is a test that is used to record the electrical activity of muscles.
When muscles are active, they produce an electrical current. This current is usually
proportional to the level of the muscle activity. An EMG is also referred to as a myogram.
EMGs can be used to detect abnormal electrical activity of muscle that can occur in many
diseases and conditions, including muscular dystrophy, inflammation of muscles, pinched nerves,
peripheral nerve damage (damage to nerves in the arms and legs),
amyotrophic lateral sclerosis
(ALS), myasthenia gravis,
disc herniation,
and others.
Why is an EMG test done?
An EMG is often performed when patients have unexplained muscle weakness. The EMG helps to
distinguish between muscle conditions in which the problem begins in the muscle and muscle
weakness due to nerve disorders. The EMG can also be used to detect true weakness, as opposed to
weakness from reduced use because of pain or lack of motivation. EMGs can also
be used to isolate the level of nerve irritation or injury.
Next: How is an intramuscular EMG done? »
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