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Nerve conduction velocity

Definition

Nerve conduction velocity (NCV) is a test of the speed of signals through a nerve.

Alternative Names

How the Test is Performed

Patches called surface electrodes, similar to those used for ECG, are placed on the skin over the nerve at various locations. Each patch gives off a very mild electrical impulse, which 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 determine the speed of the nerve signals.

Electromyography is often done at the same time as this test.

How to Prepare for the Test

Normal body temperature must be maintained (low body temperature slows nerve conduction).

Tell your doctor if you have a cardiac defibrillator or pacemaker, as precautions may need to be taken.

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 finished.

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. Occasionally, the test may be used to evaluate diseases of nerve or muscle, including myopathy, Lambert-Eaton syndrome, or myasthenia gravis.

Normal Results

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 - 4.

What Abnormal Results Mean

Most often, abnormal results are due to some sort of nerve damage or destruction, including:

• Axonopathy
• Conduction block (the impulse is blocked somewhere along the nerve pathway)
• Demyelination

The nerve damage or destruction may be due to many different conditions, including:

• Alcoholic neuropathy
• Diabetic neuropathy
• Nerve effects of uremia (from kidney failure)
• Traumatic injury to a nerve
• Guillain-Barre syndrome
• Diphtheria
• Carpal tunnel syndrome
• Brachial plexopathy
• Charcot-Marie-Tooth disease (hereditary)
• Chronic inflammatory polyneuropathy
• Common peroneal nerve dysfunction
• Distal median nerve dysfunction
• Femoral nerve dysfunction
• Friedreich's ataxia
• General paresis
• Mononeuritis multiplex
• Primary amyloid
• Radial nerve dysfunction
• Sciatic nerve dysfunction
• Secondary systemic amyloid
• Sensorimotor polyneuropathy
• 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.

Risks

There are essentially no risks.

Considerations

A NCV test shows the condition of the best surviving nerve fibers and may remain normal in some cases. A normal NCV test result can occur in some persons with significant nerve disease.

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