Nerve conduction velocity
Nerve conduction velocity (NCV) is a test to see how fast electrical signals move through a nerve. This test is done along with electromyography (EMG) to assess the muscles for abnormalities.
How the Test is Performed
Patches called surface electrodes are placed on the skin over nerves at different spots. Each patch gives off a very mild electrical impulse. This stimulates the nerve.
The nerve's 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 measure the speed of the nerve signals.
Electromyography (recording from needles placed into the muscles) is often done at the same time as this test.
How to Prepare for the Test
You must stay at a normal body temperature. Being too cold slows nerve conduction.
Tell your doctor if you have a cardiac defibrillator or pacemaker. Special steps will need to be taken before the test if you have one of these devices.
Do not wear any lotions, sunscreen, perfume, or moisturizer on your body on the day of the test.
How the Test will Feel
The impulse may feel like an electric shock. You may feel some discomfort depending on how strong the impulse is. You should feel no pain once the test is finished.
Often, the nerve conduction test is followed by electromyography (EMG). In this test, needles are placed into a muscle and you are told to contract that muscle. This process can be uncomfortable during the test. You may have muscle soreness or bruising after the test at the site where the of the needles were inserted.
Why the Test is Performed
This test is used to diagnose nerve damage or destruction. The test may sometimes be used to evaluate diseases of nerve or muscle, including:
NCV is related to the diameter of the nerve and the 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. Adult values are normally reached by age 3 or 4.
Note: Normal value ranges may vary slightly among different laboratories. Talk to your health care provider about the meaning of your specific test results.
What Abnormal Results Mean
Most often, abnormal results are due to nerve damage or destruction, including:
The nerve damage or destruction may be due to many different conditions, including:
Any peripheral neuropathy can cause abnormal results. Damage to the spinal cord and disk herniation (herniated nucleus pulposus) with nerve root compression can also cause abnormal results.
An NCV test shows the condition of the best surviving nerve fibers. Therefore, in some cases the results may be normal, even if there is nerve damage.
Griggs RC, Józefowicz RF, Aminoff MJ. Approach to the patient with neurologic disease. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 396.
Nuwer MR, Pouratian N. Monitoring of neural function: electromyography, nerve conduction, and evoked potentials. In: Winn HR, ed. Youmans and Winn Neurological Surgery. 7th ed. Philadelphia, PA: Elsevier; 2017:chap 247.
Review Date: 5/15/2017
Reviewed By: Amit M. Shelat, DO, FACP, Attending Neurologist and Assistant Professor of Clinical Neurology, SUNY Stony Brook, School of Medicine, Stony Brook, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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