Electromyogram (EMG) and Nerve Conduction Studies
An EMG is very safe. You may
get some small bruises or swelling at some of the needle sites. The needles are
sterile, so there is very little chance of getting an infection.
There is no chance of problems with nerve conduction studies. Nothing is
put into your skin, so there is no chance of infection. The voltage of
electrical pulses is not high enough to cause an injury.
Your doctor may be able to tell you
about some of the results of your nerve studies right after the tests. A full report may take 2 to 3
Electromyogram (EMG) and nerve conduction studies
The EMG recording shows no electrical activity when the
muscle is at rest. There is a smooth, wavy line on the recording with each
The nerve conduction studies show that the nerves
send electrical impulses to the muscles or along the sensory nerves at
normal speeds, or conduction velocities. Sensory nerves allow the brain to feel
pain, touch, temperature, and vibration. Different nerves have different normal
conduction velocities. Nerve conduction velocities generally get slower as a
person gets older.
Electrical activity in a muscle at rest shows that there
may be a problem with the nerve supply to the muscle. Abnormal wave lines when
a muscle contracts may mean a muscle or nerve problem, such as
amyotrophic lateral sclerosis (ALS),
post-polio syndrome, inflammation, or other muscle
In nerve conduction studies, the speed of nerve impulses is slower than what is normal for that nerve. Slower
speeds may be caused by injury to a nerve or group of nerves. Nerve
conduction velocities generally get slower as a person gets older.
The results from EMG and nerve conduction studies are used
along with your medical history, symptoms, physical and neurological exams, and
the results of other tests to help your doctor find out what the problem is or
see how a disease is changing.
What Affects the Test
Reasons you may not be able to
have the test or why the results may not be helpful include:
- Taking medicines, such as muscle relaxants and
- Having bleeding, swelling, or too much fat under the skin at the
site of the nerves or muscles being tested.
- Not being able to do what is asked during the test.
What To Think About
- The levels of some
enzymes in the blood, such as aspartate
aminotransferase (AST), lactate dehydrogenase (LDH), and creatine phosphokinase
(CPK), may rise when muscle tissue is damaged. An electromyogram can cause
higher levels of these enzymes for up to 10 days after the EMG, so blood tests
for these enzymes should not be done for 5 to 10 days after an EMG.
- Special types of electromyograms (EMG) may also be done. For example:
- Single-fiber EMG is a special type of EMG test. For this
test, very small needles are inserted into a muscle to see how a single muscle
fiber contracts. It is a useful test for
myasthenia gravis, a disease that affects the
nerve-muscle (neuromuscular) junctions.
- Repetitive nerve stimulation is a useful test for myasthenia
Lambert-Eaton syndrome. In this test, small, repeated
shocks are given to measure how the muscle reacts to repeated nerve
- External sphincter electromyogram measures the electrical
activity of the external urinary sphincter to help find urination problems. The
urinary sphincter is a ring-shaped band of muscles around the
urethra that helps control urination. The electrical
activity can be measured by skin electrodes, by needle electrodes inserted
through the skin, or by electrodes in an anal plug.