Nerve Conduction Study
The nerve conduction velocity
test is performed to evaluate nerve function. It tests the speed impulses travel
through a nerve.
Nerve conduction velocity
(NCV) is a test of the speed of conduction of impulses
through a nerve.
How the test is performed
The nerve is stimulated,
usually with surface electrodes, which are patch-like
electrodes (similar to those used for ECG) placed on the
skin over the nerve at various locations. One electrode
stimulates the nerve with a very mild electrical impulse.
The resulting electrical
activity is recorded by the other electrodes. The distance
between electrodes and the time it takes for electrical
impulses to travel between electrodes are used to calculate
the nerve conduction velocity.
Electromyography is often
done at the same time as the NCV test.
How to prepare for the
Normal body temperature
must be maintained (low body temperature slows nerve
How the test will feel
The impulse may feel like
an electric shock. Depending on how strong the stimulus is,
you will feel it to varying degrees, and it may be
uncomfortable you. You should feel no pain once the test is
Often the nerve conduction
test is followed by electromyography (EMG) which involves
needles being placed into the muscle and you contracting
that muscle. This can be uncomfortable during the test, and
you may feel muscle soreness at the site of the needles
afterwards as well.
Why the test is performed
This test is used to
diagnose nerve damage or destruction.
NCV is related to the
diameter of the nerve and the normal degree of myelination
(the presence of a myelin sheath on the axon) of the nerve.
Newborn infants have values that are approximately half that
of adults, and adult values are normally reached by age 3 -
What abnormal results mean
Most often, abnormal
results are caused by some sort of neuropathy (nerve damage
or destruction) including:
Demyelination (destruction of the myelin sheath)
Conduction block (the impulse is blocked somewhere
along the nerve pathway)
Axonopathy (damage to the nerve axon)
Some of the associated diseases or conditions include:
Nerve effects of uremia (from kidney failure)
Traumatic injury to a nerve
Carpal tunnel syndrome
Charcot-Marie-Tooth disease (hereditary)
Chronic inflammatory polyneuropathy
Common peroneal nerve dysfunction
Distal median nerve dysfunction
Femoral nerve dysfunction
Radial nerve dysfunction
Sciatic nerve dysfunction
Secondary systemic amyloid
Tibial nerve dysfunction
Ulnar nerve dysfunction
Any peripheral neuropathy can cause abnormal results, as
can damage to the spinal cord and disk herniation (herniated
nucleus pulposus) with nerve root compression.
What the risks are
There are essentially no
A NCV test shows the
condition of the best surviving nerve fibers and may remain
normal if even a few fibers are unaffected by a disease
process. A normal NCV test result can occur despite
extensive nerve damage.