Nerve conduction velocity

Definition

Nerve 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.

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

How to prepare for the test

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

Infants and children:

The preparation you can provide for this test depends on your child's age and experience. For general information regarding how you can prepare your child, see the following topics:

• Infant test or procedure preparation (birth to 1 year)
• Toddler test or procedure preparation (1 to 3 years)
• Preschooler test or procedure preparation (3 to 6 years)
• Schoolage test or procedure preparation (6 to 12 years)
• Adolescent test or procedure preparation (12 to 18 years)

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.

Normal Values

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 caused by some sort of neuropathy (nerve damage or destruction) including:

• Demyelination (destruction of the myelin sheath)
• Conduction block (the impulse is blocked somewhere along the nerve pathway)
• Axonopathy (damage to the nerve axon)

• 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
• Lambert-Eaton Syndrome
• Mononeuritis multiplex
• Primary amyloid
• Radial nerve dysfunction
• Sciatic nerve dysfunction
• Secondary systemic amyloid
• Sensorimotor polyneuropathy
• Tibial nerve dysfunction
• Ulnar nerve dysfunction

What the risks are

There are essentially no risks.

Special considerations

A NCV test shows the condition 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.

Illustrations

Nerve conduction test

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