(Electroneurography, EneG, Nerve Conduction Studies)
Nerve conduction velocity (NCV) test--also called a nerve conduction study (NCS)--is a measurement of the speed of conduction of an electrical impulse through a nerve. NCV can determine nerve damage and destruction.
During the test, the nerve is stimulated, usually with surface electrode patches attached to the skin. Two electrodes are placed on the skin over the nerve. One electrode stimulates the nerve with a very mild electrical impulse and the other electrode records it. The resulting electrical activity is recorded by another electrode. This is repeated for each nerve being tested.
The nerve conduction velocity (speed) is then calculated by measuring the distance between electrodes and the time it takes for electrical impulses to travel between electrodes.
A related procedure that may be performed is electromyography (EMG). An EMG measures the electrical activity in muscles and is often performed at the same time as NCV. Both procedures help to detect the presence, location, and extent of diseases that damage the nerves and muscles.
The nervous system is a complex, sophisticated system that regulates and coordinates body activities. It is made up of two major divisions, including the following:
The speed of nerve conduction is related to the diameter of the nerve and the degree of myelination (a myelin sheath is a type of "insulation" around the nerve). A normally functioning nerve will transmit a stronger and faster signal than a damaged nerve. This is kind of like an electric wire with rubber or plastic insulation around it. the larger the wire/electric cable, the better the insulation, the more consistent and stronger the signal.
In general, the range of normal conduction velocity will be approximately 50 to 60 meters per second. However, the normal conduction velocity may vary from one individual to another and from one nerve to another.
Abnormal results may be caused by some sort of neuropathy (damage to the nerve) that can result from a contusion or traumatic injury to a nerve. Various diseases can also cause the impulses to slow down.
Nerve conduction velocity is often used along with an EMG to differentiate a nerve disorder from a muscle disorder. NCV detects a problem with the nerve whereas an EMG detects whether the muscle is functioning properly in response to the nerve's stimulus.
Diseases or conditions that may be evaluated with NCV include, but are not limited to, the following:
Nerve conduction studies may also be performed to identify the cause of symptoms, such as numbness, tingling, and continuous pain.
There may be other reasons for your doctor to recommend NCV.
The voltage of the electrical pulses used during NCV is considered very low.
There may be risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.
Certain factors or conditions may interfere with the results of NVC test, such as damage to the spinal cord, severe pain before the test, and body temperature.
Tell your doctor if you have a cardiac defibrillator or pacemaker, as precautions may need to be taken.
A nerve conduction velocity procedure may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your doctor's practices.
The NCV is performed by a neurologist (a doctor who specializes in brain and nerve disorders), although a technologist may also perform some portions of the test.
Generally, a NCV procedure follows this process:
The paste used to attach the electrodes will be removed from your skin.
After the test, you may return to your previous activities, unless your doctor advises you differently. Your doctor may instruct you to avoid strenuous activities for the rest of the day.
Your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.
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