Nerve Conduction Velocity Test

Alternate Names
NCV
electroneurography
ENG
nerve conduction studies
stimulation myelographic study

Definition of Nerve Conduction Velocity Test

Nerve conduction velocity testing (NCV) is used to evaluate damage or disease in peripheral nerves. In this test, electrical impulses are sent down the nerves of the arms and legs. The electrical impulse is applied to one end of a nerve. The time it takes to travel to the other end of the nerve is measured.

Who is a candidate for the test?

A nerve conduction velocity test is usually ordered to diagnose or evaluate:

• weakness or numbness in an extremity
• the cause of pain
• severity of nerve injury to help determine prognosis
• response of a nerve disease or injury to treatment

How is the test performed?

NCV testing is done by a neurologist or physiatrist. It can be done in a clinic office or at the hospital bedside, and usually takes 15 to 30 minutes. A conducting paste is placed on patches called electrodes. A recording electrode is placed on the skin over the particular nerve in question. This electrode will record the activity or reaction of the nerve.

Other electrodes are placed in a particular order near the first electrode. A special instrument is used to stimulate the nerves being studied by delivering a small shock. The recording electrode records the time it takes for the shock to cause activity in the nerve and graphs the response of the nerve stimulated on a machine. The electrical stimulation may be slightly uncomfortable during the test.

What is involved in preparation for the test?

The healthcare professional may give instructions about how to prepare for a nerve conduction velocity test.

What do the test results mean?

Normal results from a nerve conduction velocity test mean that there is no evidence of damage or disease in the peripheral nerve. Nerve damage or disease may still exist despite normal NCV results. This test is often used in conjunction with electromyography (EMG) to evaluate neuromuscular abnormalities.

Abnormal results may depend on why the nerve conduction velocity test is being performed. These results may indicate:

• damage to a peripheral nerve from trauma or compression (carpal tunnel syndrome is an example)
• nerve root irritation causing weakness, numbness, or pain most commonly from a herniated disc in the neck or low back.
• polyneuropathy, a diffuse nerve damage first involving the small terminals of nerves at the feet and then progressing to involve the whole leg and the arm, most often due to diabetes mellitus
• myasthenia gravis, a disease that causes extreme muscle weakness and fatigue
• Guillain-Barré syndrome, a rapidly progressive condition that causes nerve and root damage due to inflammation with symptoms of numbness, tingling, and/or muscle weakness.
• poliomyelitis, a rare condition that affects the spinal cord