Nerve conduction velocity

Nerve conduction velocity

Definition:

An NCV is a test of the speed of conduction of impulses through a nerve.

Alternative Names:

NCV

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 nerve conduction velocity (NCV) test.

How to prepare for the test:

Normal 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:

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 given 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 (though only during the actual test and there should be no residual pain once the test is finished).

Often the nerve conduction test is followed by an EMG (electromyography) which involves needles being placed into the muscle and the patient being asked to contract that muscle. This can be uncomfortable during the test, and muscle soreness at the site of the needles may be experienced subsequently 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 (tables of normal values are used). Newborn infants have values that are approximately one-half that of adults, and adult values are normally reached by age 3 to 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)

Some of the associated diseases or conditions include:

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

Any peripheral neuropathy can cause abnormal results, as can damage to the spinal cord and disc herniation (herniated nucleus pulposus) with nerve root compression.

What the risks are:

There are essentially no risks.

Special considerations:

A 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.

Review Date: 7/26/2001
Reviewed By: Galit Kleiner-Fisman MD, FRCP(C), Department of Neurology, University of Toronto, Toronto, Ontario, Canada. Review provided by VeriMed Healthcare Network.

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