What Is a Nerve Conduction Velocity (NCV) Test?
A nerve conduction velocity (NCV) test determines how quickly electrical signals move through a particular peripheral nerve. It is also sometimes known as a nerve conduction study and is used in the diagnosis of nerve damage or nerve dysfunction.
The Purpose of an NCV Test
The peripheral nerves are the nerves outside the brain and the spinal cord. These nerves help you control your muscles and experience important senses. Healthy nerves send electrical signals more quickly and with greater strength than damaged nerves. For this reason, an NCV is helpful in determining the existence, type, and extent of nerve damage in a patient.
The NCV test allows the physician to tell the difference between an injury to the nerve axon (the nerve fiber) and an injury to the myelin sheath—the protective covering surrounding the nerve. It is also useful for telling the difference between a nerve disorder and a condition where nerve injury has affected the muscles. Being able to make these distinctions is important for diagnosis and for determining an appropriate course of treatment.
There are no known risks associated with this test.
When Is This Test Necessary?
This test is useful for diagnosing a variety of different muscular and neuromuscular disorders. A doctor may use this test if they suspect a pinched nerve. Alternately, they may use it if they wish to check for the presence of a nerve disease.
The test is often performed with an electromyography (EMG), which is a test that records electrical signals moving through the muscles.
Preparing for a NCV Test | Preparation
Going into the test, it is important that you have a normal body temperature. This is because a low body temperature slows down nerve conduction. If the weather is very cold, for instance, your doctor may have you sit in a warm room for a few minutes before the test.
If you use a pacemaker or cardiac defibrillator, your physician should be made aware. The electrodes used in the test could affect the electronic impulses of your medical device.
How a NCV Test is Performed
Flat, patch-style electrodes are placed on the skin at intervals over the nerve that is being examined. These electrodes give off low-intensity electrical impulses, which stimulate the nerve. This stimulation may feel like a slight electric shock, though it is not particularly painful.
The impulses produced by this electrical current are viewed on an oscilloscope or computer screen. This monitoring system allows the physician to determine how fast the impulses are traveling through the nerves.
Understanding the Test Results
If the response from the electrical current is slower than is normal, this is a likely sign of damage to the myelin sheath. On the other hand, if the response shows a decreased response but with a normal speed, there is probably damage to the nerve fiber.
The results of this test, as well as the cause of the nerve damage, will help determine a proper course of treatment.
A few of the possible causes for abnormal results on this test are:
- axonopathy (damage to the nerve cell)
- conduction block (an obstacle to the impulse within the nerve)
- demyelination (damage to the myelin sheath)
There are a number of different conditions that may result in these causes, including:
- alcoholic neuropathy
- brachial plexopathy
- diabetic neuropathy
- femoral nerve dysfunction
- general paresis
- Guillain-Barre syndrome
If the cause of the nerve damage is known and understood, addressing the cause should make your symptoms better. Some possible treatments for nerve damage include physical therapy, surgery, and pain medications. The best treatment depends on the severity, extent, and type of nerve damage.