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EMG stands for
electromyogram
(the result of the test).
An EMG, used in conjunction with a neurological
examination, helps establish a diagnosis and the extent of a problem by
measuring the electrical activity of a muscle in response to stimulation.
An EMG is done by inserting electrodes in fine needles into
the muscles being tested, and by placing electrodes on the skin over peripheral
nerves.
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The presence, size, and shape of the
wave form produced on the oscilloscope (the action potential)
provide information about the ability of the muscle to respond to
nervous stimulation. |
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Each muscle fiber that contracts
will produce an action potential, and the size of the muscle fiber
affects the rate (how frequently an action potential occurs) and
size (amplitude) of the action potential(s). |
An EMG may be used to evaluate a variety of problems,
including the following:
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Nerve damage from compression by a disk in the neck
or the back
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Nerve compression from carpal tunnel syndrome
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Neuromuscular diseases such as amyotrophic lateral
sclerosis (ALS), poliomyelitis, myasthenia gravis and muscular dystrophy
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Peripheral neuropathy caused by such conditions as
diabetes, pernicious anemia and heavy metal toxicity |
In many instances, an EMG can provide critical diagnostic
information that can not be obtained in any other way.
Although there is some discomfort associated with the
procedure, an EMG is usually done on an outpatient basis.
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No special
preparation is usually necessary.
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A needle electrode
is inserted through the skin into the muscle. |
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The electrical
activity detected by this electrode is displayed on an oscilloscope. |
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You may be asked
to contract the muscle.
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| There may be some discomfort
with insertion of the electrodes. |
| Afterward, the examined muscle
may feel tender or bruised. |
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