Electromyography (EMG) and Nerve Conduction Velocity (NCV)
Tests
What is it?
Electromyography (EMG) is a test of a muscle’s
electrical activity. It is used to test how a muscle
responds to signals from the nerves responsible for muscle
movement, called motor nerves. An EMG may also include a
test of how fast the motor nerve conducts impulses. This
is called a nerve conduction study (NCS) or nerve
conduction velocity (NCV) test.
Who needs this procedure?
An EMG is ordered when patients have symptoms such as
muscle weakness, stiffness, or atrophy. This test is often
used to diagnose muscle and nerve disorders such as
amyotrophic lateral sclerosis (ALS), myasthenia gravis,
muscular dystrophy, myotonia, neuropathies, and myopathies.
NCV is used to help make a diagnosis when the primary
symptoms involve sensations such as pain, tingling, and
numbness, rather than weakness.
How do I prepare for this procedure?
Your doctor will advise you not to take any stimulant
drugs, drink beverages like coffee, tea, or cola, or take
any medication that has a sedating effect for at least 24
hours before the test. Make sure your doctor knows of any
heart conditions such as a pacemaker, which could be
affected by the small electrical impulses sent to the
nerve during a nerve conduction velocity (NCV) test. Also
make your doctor aware if you are taking any blood
thinning medication (anticoagulants) or if you have a
bleeding disorder because fine needles are inserted into
the muscles to conduct the electrical impulse.
How is this procedure performed?
You will most likely put on a hospital gown to provide
easy access to the areas being tested. Then you will be
put into a position in which the muscle being tested is at
rest, either lying down or sitting. You may feel some
discomfort as a very fine needle is inserted into the
muscle being tested. The needle is an electrode, which
will transmit the muscle’s electrical activity to a
recording device. The technician will direct you to move
the muscle in various ways to tighten and relax it. The
muscle’s response to movement and rest is recorded so your
doctor can study the pattern for normal or abnormal
electrical activity. If you are also having an NCV test, a
very small electrical shock is delivered to the nerve
through an electrode that transmits the nerve’s response
to the recording device. An EMG takes anywhere from 30 to
90 minutes.
What can I expect after the procedure?
You may feel some soreness or notice some bruising in
the muscles tested for a few days after an EMG. There may
also be some minor bleeding around the needle insertion
points for a few hours after the test. Notify your doctor
if these conditions do not improve within these
timeframes.
This information has been designed as a comprehensive and quick reference
guide written by our health care reviewers. The health information written
by our authors is intended to be a supplement to the care provided by your
physician. It is not intended nor implied to be a substitute for
professional medical advice.
|
