Definition of Nerve conduction velocity test
Nerve conduction velocity
test: An electrical test used to detect nerve conditions. In the nerve
conduction velocity (NCV) test, the nerve is electrically stimulated by one electrode while other electrodes detect the electrical impulse "down stream" from the first electrode. The NCV test is usually done with surface patch electrodes similar to those used for an EKG (electrocardiogram). The patch electrodes are 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 speed of impulse transmission (the nerve conduction velocity, or NCV).
A decreased speed of nerve conduction indicates nerve
disease. The NCV test is often done at the same time as an electromyogram (EMG) in order to
exclude or detect both nerve and muscle conditions. The interpretation of an
abnormal NCV test depends on why the test was done in the first place. It may
indicate damage to a nerve from trauma, polio, diabetic neuropathy (nerve damage), a herniated disc, myasthenia gravis, Guillain-Barre
syndrome, polyneuropathy (the simultaneous malfunction of many nerves). and many other conditions.
The patient having a NCV test lies on an examination
table. The electrodes are placed on the skin over the nerve to be studied. 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. The NCV test
is also called a nerve conduction study, or NCS.
Last Editorial Review: 7/11/2004
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