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Nerve conduction velocity
DefinitionNerve 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.
How to prepare for the testNormal body temperature must be maintained (low body temperature slows nerve conduction).
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
How the test will feel
The impulse may feel like an electric shock. Depending on how strong the stimulus is, the patient will feel it to varying degrees. It may be uncomfortable for some patients during the actual test. There should be no residual pain once the test is finished.
Often the nerve conduction test is followed by electromyography (EMG) which involves needles being placed into the muscle and the patient contracting that muscle. This can be uncomfortable during the test, and muscle soreness at the site of the needles may be experienced afterwards as well.
Why the test is performedThis test is used to diagnose nerve damage or destruction.
Normal ValuesNCV 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 to 4.
What abnormal results meanMost often, abnormal results are caused by some sort of neuropathy (nerve damage or destruction) including:
What the risks areThere are essentially no risks.
Special considerationsA NCV test reflects the status 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.
Update Date: 5/8/2003Elaine T. Kiriakopoulos, M.D., M.Sc., Department of Neurology, Beth Israel Deaconess Medical Center, Harvard University, Boston, MA. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT