(Electroneurography, EneG, Nerve Conduction Studies)
What is nerve conduction velocity?
Nerve conduction velocity (NCV) test 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. Please see this procedure for additional information.
Anatomy of the nervous system:
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:
central nervous system - consisting of the brain and spinal cord.
peripheral nervous system - consisting of all other neural elements.
Interpretation of the test results:
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.
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.
Reasons for the Procedure
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:
Guillain-Barré syndrome - a condition in which the body's immune system attacks part of the peripheral nervous system. The first symptoms may include weakness or tingling sensations in the legs.
carpal tunnel syndrome - a condition in which the median nerve, which runs from the forearm into the hand, becomes pressed or squeezed at the wrist by enlarged tendons or ligaments. This results in pain and numbness in the fingers.
Charcot-Marie-Tooth disease - a hereditary neurological condition that affects both the motor and sensory nerves. One characteristic is weakness of the foot and lower leg muscles.
herniated disc disease
chronic inflammatory polyneuropathy and neuropathy - conditions resulting from diabetes or alcoholism
sciatic nerve problems
peripheral nerve injury
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 physician to recommend NCV.
Risks of the Procedure
The voltage of the electrical pulses used during NCV is considered very low.
There may be risks depending upon your specific medical condition. Be sure to discuss any concerns with your physician prior to the procedure.