Nerve conduction velocity (NCV) is a test to see how fast electrical signals move through a nerve.

How is the NCV Test Performed?

Patches called surface electrodes, similar to those used for ECG, are placed on the skin over nerves 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 (recording from needles placed into the muscles) is often done at the same time as this test.

How Can I Prepare for the NCV 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.

What does the NCV Test Feel Like?

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 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 have muscle soreness after the test at the site of the needles.

Why is the NCV Test 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.

What do Normal NCV Test Results Look Like?

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, and adult values are normally reached by age 3 or 4.

Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What can Abnormal Results Mean for Me?

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

Axonopathy (damage to the long portion of the nerve cell)
Conduction block (the impulse is blocked somewhere along the nerve pathway)
Demyelination (damage and loss of the fatty insulation surrounding the nerve cell)
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 amyloidosis
• Radial nerve dysfunction
• Sciatic nerve dysfunction
• Secondary systemic amyloidosis
• 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.

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