Nerve conduction velocity
Nerve conduction velocity (NCV) is a test of the speed of conduction of impulses through a nerve.
How the test is performed
The nerve is stimulated, usually with surface electrodes, which are patch-like electrodes (similar to those used for ECG) placed on the skin over the nerve at various locations. One electrode stimulates the nerve with a very mild electrical impulse.
The resulting electrical activity is recorded by the other electrodes. The distance between electrodes and the time it takes for electrical impulses to travel between electrodes are used to calculate the nerve conduction velocity.
Electromyography is often done at the same time as the NCV test.
How to prepare for the test
Normal body temperature must be maintained (low body temperature slows nerve conduction).
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child’s age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child’s age:
- Infant test or procedure preparation (birth to 1 year)
- Toddler test or procedure preparation (1 to 3 years)
- Preschooler test or procedure preparation (3 to 6 years)
- School age test or procedure preparation (6 to 12 years)
- Adolescent test or procedure preparation (12 to 18 years)
How the test will feel
The impulse may feel like an electric shock. Depending on how strong the stimulus is, the patient will feel it to varying degrees. It may be uncomfortable for some patients during the actual test. There should be no residual pain once the test is finished.
Often the nerve conduction test is followed by electromyography (EMG) which involves needles being placed into the muscle and the patient contracting that muscle. This can be uncomfortable during the test, and muscle soreness at the site of the needles may be experienced afterwards as well.
Why the test is performed
This test is used to diagnose nerve damage or destruction.
NCV is related to the diameter of the nerve and the normal 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, and adult values are normally reached by age 3 to 4.
What abnormal results mean
Most often, abnormal results are caused by some sort of neuropathy (nerve damage or destruction) including:
- Demyelination (destruction of the myelin sheath)
- Conduction block (the impulse is blocked somewhere along the nerve pathway)
- Axonopathy (damage to the nerve axon)
Some of the associated diseases or conditions include:
- Alcoholic neuropathy
- Diabetic neuropathy
- Nerve effects of uremia (from Kidney failure)
- Traumatic injury to a nerve
- Guillain-Barre syndrome
- Carpal tunnel syndrome
- Brachial plexopathy
- Charcot-Marie-Tooth disease (hereditary)
- Chronic inflammatory polyneuropathy
- Common peroneal nerve dysfunction
- Distal median nerve dysfunction
- Femoral nerve dysfunction
- Friedreich’s ataxia
- General paresis
- Lambert-Eaton Syndrome
- Mononeuritis multiplex
- Primary amyloid
- Radial nerve dysfunction
- Sciatic nerve dysfunction
- Secondary systemic amyloid
- Sensorimotor polyneuropathy
- Tibial nerve dysfunction
- Ulnar nerve dysfunction
Any peripheral neuropathy can cause abnormal results, as can damage to the spinal cord and disc herniation (herniated nucleus pulposus) with nerve root compression.
What the risks are
There are essentially no risks.
A NCV test reflects the status of the “best” surviving nerve fibers and may remain normal if even a few fibers are unaffected by a disease process. A normal NCV test result can occur despite extensive nerve damage.
by Harutyun Medina, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.