A nerve conduction velocity test, often abbreviated as NCV, measures the speed at which an electrical signal travels through a nerve. It is often used to diagnose nerve disorders or injuries. The test uses electrodes, similar to those used for an electrocardiogram, that give off a mild electrical pulse, which in turn stimulates the nerve. The time it takes for an electrical impulse to travel from one electrode to the next indicates the speed of nerve conduction.
Damaged nerves usually conduct signals at a lower speed and strength than healthy nerves. Although nerve velocity is influenced by the insulating myelin sheath, most neuropathies are caused by damage to the axon, or long portion, of the nerve cell. Abnormal results typically indicate nerve damage, such as axonopathy, or damage to the axon; demyelination, or damage to or loss of the myelin sheath; or a conduction block. The nerve conduction velocity test can usually differentiate between axon and myelin damage.
If a person experiences tingling, numbness, pain, weakness, or other symptoms, a nerve conduction velocity test may be ordered. The test is usually performed in a neurologist’s office by a specially trained technician or other health care professional. Because nerve conduction can be slowed by low body temperature, normal temperature must be maintained throughout the test. The patches attached to electrodes are placed on the patient’s skin at various locations, and a low intensity electric current is introduced to stimulate the nerves. Discomfort is usually minimal and dissipates as soon as the test is complete.
The test is often followed by an electromyogram, which measures electric activity in muscles, in order to detect or rule out muscular disorders or damage. During an electromyogram, needles are inserted into the muscles at various places and the patient contracts those muscles. This test can be painful, and afterward patients may experience muscle soreness.
Based on the results of the nerve conduction test as well as the information gleaned from the electromyogram, a neurologist can diagnose or exclude various disorders or injuries. Any type of spinal cord injury or nerve root compression can cause abnormal results. Other disorders that involve nerve damage or destruction include alcoholic or diabetic neuropathy, carpal tunnel syndrome, and Guillain-Barre syndrome, which is an auto-immune disorder that often causes paralysis. A nerve conduction velocity test also may be use to diagnose multiple sclerosis, sciatic nerve dysfunction, brachial plexopathy and diphtheria. Since the test measures the performance of surviving nerve fibers, it is possible that nerve damage may exist and not be detected. Additional testing methods or other diagnostic tools may be used for further investigation.