Alternative Names NCV, electroneurography, ENG, stimulation myelographic study
Definition Nerve conduction studies are 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 studies test is usually ordered to diagnose or evaluate:
nerve injury in a person who has weakness in an extremity
nerve injury or disease, as opposed to muscular injury or disease
the severity of nerve injury
the response of a nerve disease or injury to treatment
How is the test performed? NCV testing is done by a neurologist. It can done in a nerve study 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.
The time is sent to a machine called an oscilloscope. This machine can measure the response time of the nerve to stimulation. A calculation is then done on the response time and the distance between the electrodes. The electrical stimulation may be slightly uncomfortable during the test.
What is involved in preparation for the test? The doctor may give instructions about how to prepare for a nerve conduction studies test.
What do the test results mean? Normal results from a nerve conduction studies 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 is because other healthy fibres in the same nerve may show a normal reaction time. This test is often used in conjunction with electromyography (EMG) to evaluate neuromuscular abnormalities.
Abnormal results may depend on why the nerve conduction studies test is being performed. These results may indicate:
peripheral nerve injury or disease
carpal tunnel syndrome, a condition in which pressure on the median nerve in the wrist leads to pain or numbness in the fingers
poliomyelitis, a condition that affects the spinal cord
myasthenia gravis, a disease that causes extreme muscle weakness and fatigue
Guillain-Barre syndrome, a condition that causes nerve damage and inflammation, and muscle weakness and paralysis
damage to a nerve from trauma
nerve defects from kidney disease or damage
chronic inflammatory polyneuropathy, which is the simultaneous malfunction of many peripheral nerves throughout the body. It can be caused by diabetes, chronic renal failure, or severe malnutrition.
metachromatic leukodystrophy, a very serious condition that causes difficulty walking and difficulty controlling movements of the arms and legs
Author: Eileen McLaughlin, RN, BSN Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 6/06/2005 Contributors Potential conflict of interest information for reviewers available on request
