Nerve conduction velocity: Side effects and normal values
In this article, learn about how a nerve conduction velocity or NCV test is used, what the normal results look like, and whether there are any side effects.
NCV as a diagnostic tool
An NCV test may be used to diagnose nerve damage.
Image credit: Kiwi-sonja, (2008, June 6).
The purpose of an NCV test is to look for nerve damage. During the test, a nerve is directly stimulated with an electrical current to see how it reacts. NCV tests can help diagnose a variety of muscular and neuromuscular conditions.
Sometimes, NCV tests are done in conjunction with electromyograms or EMGs. Doctors use EMGs, as well, to help diagnose neurological or muscular diseases.
An EMG can detect whether a muscle is responding properly to nerve signals, which can help determine whether a person has a nerve disease or a muscle condition.
An NCV test may be used to diagnose the following conditions:
Herniated disk disease
Herniated disk disease refers to problems with the rubber cushions or disks between the vertebrae. The vertebrae are the individual bones that make up the spine.
Herniated disks affect nearby nerves and can cause irritation, pain, weakness, and numbness in the legs and arms. Most herniated disks affect the lumbar spine (lower back), but they can also affect the cervical spine (the neck).
Sciatica nerve problems
Sciatica is a condition that affects the sciatic nerve, which is the largest nerve in the human body.
The sciatic nerve extends from the lower back and down both sides of the hips, buttocks, legs, and feet.
Sciatic nerve pain is often related to herniated disks in the low back and low spine. According to one study, 42 percent of participants with sciatica had back pain. Out of those with back pain, 68 percent also had herniated disks.
Sciatic nerve pain and herniated disks often coincide because when disks in the lower spine and back slip out of place, they put pressure on the nerves around the disk.
Sciatic nerve pain radiates from the lower back into the legs. Pain can be mild or severe. Weakness, numbness, and tingling in the legs and feet are also common.
An NCV test can help diagnose compression or damage in the sciatic nerve. It can also detect any problems with the nerve itself.
Both EMGs and NCVs are useful for determining the cause of sciatic nerve pain, such as a herniated disk.
Peripheral neuropathy affects the nerves that send information to and from the brain and spinal cord.
At least 20 million people in the United States are affected by some form of peripheral neuropathy, according to the National Institute of Neurological Disorders and Stroke.
The peripheral nerves are responsible for sending information from the brain and spinal cord to the rest of the body, and vice versa.
When peripheral nerves are damaged, people may feel weakness, numbness, and pain in their hands and feet. While these are the most common locations for symptoms, they can also occur elsewhere.
NCV tests can measure the extent of the damage to the nerve fibers.
Carpal tunnel syndrome
Carpal tunnel syndrome (CTS) occurs when the median nerve, which runs from the forearm into the hand, becomes compressed at the wrist.
Symptoms of CTS include numbness, tingling, and pain in the thumb and fingers that may extend into the arm. CTS may eventually lead to nerve damage and affect a person's ability to grip or hold objects.
An NCV test can check nerve function in the median nerve and help a doctor determine the right treatment plan.
Guillain-Barré syndrome (GBS) is an autoimmune disease that occurs when the body's immune system attacks parts of the peripheral nervous system.
The first signs of GBS are weakness and tingling in the legs. Recovery from GBS is slow, but most people recover fully. The most severe cases, however, may cause paralysis and disability.
An NCV test can help diagnose GBS. Electrical signals along nerves affected by GBS are slower than others.
How to prepare
The doctor performing the NCV test will explain the procedure and give the person an opportunity to ask questions.
To prepare, people may need to do the following:
- Stop using lotions, oils, perfumes, or other products on the skin for several days prior to the test.
- Tell their doctor about any medications they currently take, including over-the-counter painkillers and supplements.
- Dress in loose clothing or easily removable layers.
- Inform the doctor if they have a pacemaker or cardiac defibrillator.
There is no sedation or fasting required for an NCV test, although some people may need to take additional precautions based on any existing health conditions they have.
What to expect
A person undergoing the NCV test may be asked to remove all jewellery and wear a hospital gown.
NCV tests are usually outpatient procedures, meaning they do not require an overnight stay at the hospital.
Prior the procedure, a doctor will ask a person to:
- remove clothing, jewelry, eyeglasses, hairpins, and other metal objects that may affect the test
- wear a hospital gown
- sit or lie down, depending what body part is being tested
Once the person is ready, a doctor will locate the nerves and attach a recording electrode to the skin over the nerves.
A second electrode will be placed a short distance away. This second electrode will produce a mild and brief electric shock to stimulate the nerve. It should not be painful but may cause minor discomfort. There will be no pain after the test is complete.
The stimulation and nerve response will appear on a monitor for a doctor to record.
A person may need to do an EMG test following the NCV test. During an EMG test, needles are put into the muscles, and the person will then stretch the muscles to test their function. This can be uncomfortable and may cause soreness and bruises at the needle sites.
Are there any risks?
The voltage used in NCV testing is very low, and risks are minimal. However, it is essential to discuss any concerns with the doctor requesting the procedure.
People with pacemakers or cardiac defibrillators may need to take extra precautions when doing an NCV test.
Some additional factors, including pain before the procedure and body temperature, may affect test results.
NCV tests can measure the speed and strength of nerve signals. Nerve conduction velocity between 50 to 60 meters per second is considered normal.
A damaged nerve may send a slower and weaker signal than a healthy one. It is possible to have normal results even if a person has nerve damage.
Anyone concerned about their NCV test results should speak with a doctor for individualized diagnosis and treatment.