Nerve Conduction Velocity
What is a nerve conduction velocity test?
A nerve conduction velocity (NCV)
test measures how fast an electrical impulse moves through your nerve. NCV can identify
nerve damage. This test is also called a nerve conduction study (NCS).
During the test, your nerve is
stimulated, often with electrode patches put on 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.
The speed is then calculated by measuring the distance between electrodes and the time it takes for electrical impulses to travel between electrodes.
A related test that may be done is
an electromyography (EMG). This measures the electrical activity in your muscles. It
should usually be done at the same time as an NCV. Both tests help find the presence,
location, and extent of diseases that damage the nerves and muscles.
Why might I need a nerve conduction velocity test?
NCV is often used along with an EMG
to tell the difference between a nerve disorder and a muscle disorder. NCV detects a
problem with the nerve, whereas an EMG detects whether the muscle is working the right
way in response to the nerve’s stimulus.
Diseases or health problems that
may be checked with NCV include:
- 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 health
problem 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 health
problem 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. It causes pain and damage to
Nerve damage (neuropathy). This
condition may occur from many health issues, such as diabetes, chemotherapy
treatment, autoimmune disorders like chronic inflammatory demyelinating neuropathy,
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.
Nerve conduction studies may also
be done to find the cause of symptoms, such as numbness, tingling, and ongoing pain.
Other health problems may prompt
your healthcare provider to recommend NCV.
What are the risks of NCV tests?
The voltage of the electrical
pulses used during an NCV is considered very low. There are no known long-term side
effects of NCV testing. The main side effect is short-term discomfort from the
Tell your healthcare provider if
you have a cardiac defibrillator or pacemaker. If you have one of these, precautions may
need to be taken. Risks depend on your specific health problem. Be sure to discuss any
concerns with your healthcare provider before the procedure.
Certain factors or conditions may
interfere with the results of NCV tests. This includes damage to the spinal cord, severe
pain before the test, and body temperature.
How do I get ready for an NCV test?
- Your healthcare provider will explain the procedure and you can ask questions.
- You may be asked to sign a consent
form that gives your permission to do the procedure. Read the form carefully and ask
questions if something is not clear.
- Generally, you will not need to fast or get sedation before the procedure.
- Normal body temperature must be
maintained before and during the procedure. Low body temperature slows nerve
- Tell your healthcare provider of all
medicines (prescription and over-the-counter) and herbal supplements that you take.
For some conditions, certain medicines may need to be adjusted.
- Dress in clothes that allow access to the area to be tested or that are easily removed.
- Stop using lotions or oils on your skin for a few days before your procedure.
- Based on your health problem,
your healthcare provider may request other preparations. Let him or her know if you
are taking blood-thinning medicines
What happens during the NCV test?
An NCV procedure may be done on an
outpatient basis, or as part of your stay in a hospital. Procedures may vary depending
on your condition and your healthcare provider’s practices.
The NCV is done by a neurologist.
This is a healthcare provider 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. The number of nerves tested depends on your case and what the provider
is looking for.
- 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
- 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.