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EMG AND NCS
 Electromyography
(EMG) and Nerve Conduction Studies(NCS) are ordered to learn
more about the health of peripheral nerves, in other words,
the nerves that travel to and from your hands and feet. These
tests can establish if a nerve is working properly by measuring
the speed of the nerve's conductivity and the electrical activity
of the nerve. In the case of nerve injury or nerve entrapment
the test can often locate the exact site. EMG NCS are often
done together to provide more complete information.
EMG
The muscles are assessed by inserting
a tiny Teflon coated pin electrode into the muscle with the
computer then recording the muscle potential. The sensation
is similar to that of an injection that goes into the muscle
as the pin electrode is inserted into the muscle. (That is
if sensory awareness is not a problem.) It is important for
the patient to lie still to reduce interference and to achieve
accurate readings.
NCS
The patient will be asked to lie on
an examination table. Electrodes are placed on the skin over
the nerve to be studied. These electrodes act as microphones
to pick up any electrical signal that goes by them. An electrical
stimulator is then placed on the skin near the electrodes
and is used to create an electrical current strong enough
to fully stimulate the nerve. A computer is used to record
responses as various nerves are tested. This allows the physician
to measure and calculate how fast the nerve is sending the
impulses to the muscle.
PREPARATION:
- Please do not wear any lotion or
perfume anywhere on the body.
- Wear loose fitting clothes that
can be raised to above the knee or above the elbow, depending
on the limb that will be tested.
- Take all medications regularly,
unless given other instructions by your physician.
Commonly asked questions:
1. Does it hurt?
Parts of the test are uncomfortable
but not severely painful. The anxiety before the test can
be more of a factor than the test itself. A majority of the
time spent with the patient is setting up the studies and
running the computer; a very small amount of the time involves
electrical stimulation or use of the pin electrode. The electrical
stimulation of the nerve conduction study could be compared
to a static electricity shock from a doorknob after walking
across carpet. The pin insertion could be compared to being
pinched by someone's fingernails.
2. Is sedation or anesthesia used?
No, the test is well tolerated and
the patient needs to be awake to follow instructions during
the exam.
3. Are there any side effects?
There can be minor irritation at the
pin insertion sites but otherwise, there are no lasting effects
from either the NCS or the EMG.
4. Will I get results of the test that
day?
The examining physician can give you
an idea of any obvious abnormalities at the end of the test.
However, more detailed interpretation will be done at a later
time with a full report sent to the physician who referred
the patient.
The results from EMG and nerve conduction studies are usually
not enough on their own to diagnose a condition. They can
be used along with a person's history, symptoms, physical
and neurological examinations, and the results of other tests
to help establish a diagnosis.
5. Why is it done?
Nerve conduction studies are done to:
- Detect and evaluate damage to the
peripheral nervous system (which includes all the nerves
that lead away from the brain and spinal cord and the smaller
nerves that branch out from those nerves).
- Identify the location of abnormal
sensations, such as numbness, tingling, or pain.
Electromyography (EMG) is done to:
- Aid in diagnosis of conditions that
damage muscle tissue, nerves, or the junctions between nerve
and muscle (neuromuscular junctions).
- Evaluate the cause of weakness,
paralysis, involuntary muscle twitching, or other symptoms.
Problems in a muscle, the nerves supplying a muscle, the
spinal cord, or the area of the brain that controls a muscle
can all cause these kinds of symptoms.
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