Normal nerve conduction velocity of radial nerve is essential for differential diagnosis of various type of radial neuropathies, C7 radiculopathy and nerve lesion. There are various conditions which affect Nerve Conduction Velocity (NCV) like age, upper and lower limb, temperature, hence there cannot be a universal one reference value of a particular nerve taking into consideration of geographical variation of climate in the world. Therefore different regions and labs have their own standard reference value.
How does an NCV test work?
A nerve conduction velocity (NCV) test is used to assess nerve damage and dysfunction. Also known as a nerve conduction study, the procedure measures how quickly electrical signals move through your peripheral nerves.
Your peripheral nerves are located outside of your brain and along your spinal cord. These nerves help you control your muscles and experience the senses. Healthy nerves send electrical signals more quickly and with greater strength than damaged nerves.
The NVC test helps your doctor differentiate between an injury to the nerve fiber and an injury to the myelin sheath, the protective covering surrounding the nerve. It can also help your doctor tell the difference between a nerve disorder and a condition where a nerve injury has affected the muscles. Making these distinctions is important for proper diagnosis and determining your course of treatment.
During the test, your nerve is stimulated, usually with electrode patches attached to your skin. Two electrodes are placed on the skin over your nerve. One electrode stimulates your nerve with a very mild electrical impulse. The other electrode records it. The resulting electrical activity is recorded by another electrode. This is repeated for each nerve being tested.
What Diseases can be checked by NCV Test?
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 a tingling sensation 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 causes pain and numbness in the fingers.
Charcot-Marie-Tooth disease. An inherited neurological condition that affects both the motor and sensory nerves. It causes weakness of the foot and lower leg muscles.
Herniated disk disease. This condition occurs when the fibrous cartilage that surrounds the disks of your vertebrae breaks down. The center of each disk, which contains a gelatinous substance, is forced outward. This places pressure on a spinal nerve and causes pain and damage to the nerve.
Chronic inflammatory polyneuropathy and neuropathy. These are conditions resulting from diabetes or alcoholism. Symptoms may include numbness or tingling in a single nerve or many nerves at the same time.
Sciatic nerve problems. There are many causes of sciatic nerve problems. The most common is a bulging or ruptured spinal disk that presses against the roots of the nerve leading to the sciatic nerve. Pain, tingling, or numbness often result.
Myasthenia Gravis. Myasthenia gravis is a chronic autoimmune neuromuscular disease that causes weakness in the skeletal muscles, which are responsible for breathing and moving parts of the body, including the arms and legs.
Tarsal Tunnel Syndrome. Tarsal tunnel syndrome is a condition caused by repeated pressure that results in damage on the posterior tibial nerve. Your tibial nerve branches off of the sciatic nerve and is found near your ankle.
Bell Palsy. Bell’s palsy is a form of temporary facial paralysis resulting from damage or trauma to the facial nerves. The facial nerve-also called the 7th cranial nerve-travels through a narrow, bony canal (called the Fallopian canal) in the skull, beneath the ear, to the muscles on each side of the face. For most of its journey, the nerve is encased in this bony shell.
Myopathy. A myopathy is a muscle disease unrelated to any disorder of innervation or neuromuscular junction. These conditions have widely varying etiologies, including congenital or inherited, idiopathic, infectious, metabolic, inflammatory, endocrine, and drug-induced or toxic.
Nerve conduction studies may also be done to find the cause of symptoms, such as numbness, tingling, and continuous pain.
How’s Test Performed?
The NCV is done by a neurologist. This is a doctor who specializes in brain and nerve disorders. A technologist may also do some parts of the test.
Generally, an NCV procedure follows this process:
You will be asked to remove any clothing, jewelry, hairpins, eyeglasses, hearing aids, or other metal objects that may interfere with the procedure.
If you are asked to remove clothing, you will be given a gown to wear.
You will be asked to sit or lie down for the test.
A neurologist will locate the nerve(s) to be studied.
A healthcare provider will attach a recording electrode to the skin over your nerve, using a special paste. He or she will then place a stimulating electrode away from the recording electrode, at a known distance.
A mild and brief electrical shock, given through the stimulating electrode, will stimulate your nerve.
You may experience minor discomfort for a few seconds.
The stimulation of the nerve and the response will be displayed on a monitor.
The entire test may take 20 to 30 minutes. The sensation may be uncomfortable, but it typically isn’t painful.
Your doctor may want to perform the test in more than one location. In one study, researchers used the NCV test to examine damage to the ulnar nerve, which provides sensation to the hands and feet. Adding a third stimulation site to the two normally used increased the sensitivity of the test from 80 to 96 percent.
Analyzing the Results
NCV is related to the diameter of the nerve and the degree of myelination (the presence of a myelin sheath on the axon) of the nerve. Newborn infants have values that are approximately half that of adults. Adult values are normally reached by age 3 or 4.
Note: Normal value ranges may vary slightly among different laboratories. Talk to your health care provider about the meaning of your specific test results.
What Abnormal Results Mean
Most often, abnormal results are due to nerve damage or destruction, including:
Axonopathy (damage to the long portion of the nerve cell)
Conduction block (the impulse is blocked somewhere along the nerve pathway)
Demyelination (damage and loss of the fatty insulation surrounding the nerve cell)
The nerve damage or destruction may be due to many different conditions, including:
Nerve effects of uremia (from kidney failure)
Traumatic injury to a nerve
Carpal tunnel syndrome
Charcot-Marie-Tooth disease (hereditary)
Chronic inflammatory polyneuropathy
Common peroneal nerve dysfunction
Distal median nerve dysfunction
Femoral nerve dysfunction
Radial nerve dysfunction
Sciatic nerve dysfunction
Secondary systemic amyloidosis
Tibial nerve dysfunction
Ulnar nerve dysfunction
Any peripheral neuropathy can cause abnormal results. Damage to the spinal cord and disk herniation (herniated nucleus pulposus) with nerve root compression can also cause abnormal results.