A Patient's Guide to Electromyograms
What it is: An electromyogram (EMG) test looks at the function of the
nerve roots leaving the spine. It does this by looking at how well the electrical
currents in the nerves are being transmitted to the muscles. Pressure on the
nerves or damage to the nerves changes the way they transmit electrical current.
This shows up in the muscles as they react to the information being sent to
them from the brain - by the nerves.
What the test shows: By looking for abnormal electrical signals in the
muscles, the EMG can show if a nerve is being irritated, or pinched as it leaves
the spine. Think of how you test the wiring on a lamp. If you place a working
bulb into the lamp, and the bulb lights up, you assume that the wiring is okay.
However, what if the bulb does not light up? You can safely assume that something
is probably wrong with the wiring, like the lamp is unplugged, or a short circuit
has occurred. By using the muscles like the light bulb in the lamp, the EMG
is able to determine the condition of the nerves that supply those muscles,
like the wiring on the lamp. If the EMG machine finds that the muscles (the
light bulb) are not working properly, the doctor can assume that the nerves
(the wiring) must be getting pinched somewhere.
What the test does not show: These tests do not show why the problem
occurred or what is causing the problem. The EMG test looks primarily at how
the muscles are reacting to the nerve problem (the wiring problem). There could
be a problem in the nerve somewhere between the spine and the muscle. The problem
may not necessarily be in the spine itself. Still, it is a good test to see
how much the nerve is being damaged, and if there is a herniated disc or other
source of pressure on the nerve roots.
How the test is done: The test is done by inserting tiny electrodes
into the muscles of the lower extremity. Very small needles are inserted through
the skin and down into the muscles.
What risks the test has: There are not many risks associated with the
EMG or SSP tests. Anytime a needle is inserted into the body there is a small
chance of infection - but the risk is almost zero in this type of test.
What the test costs: An EMG/SSP usually has two costs associated with
the test. The first cost is the fee for actually doing the test. This is called
the "technical fee". The second cost is the fee of having a specialist, such
as a neurologist, to read and interpret the test. This is called the "professional
fee". You may get two bills for this test: one from the hospital or clinic where
you had the EMG/SSP done, and one from the specialist who read the test.
Copyright © 2003 DePuy Acromed.
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