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Nerve conduction test
Nerve conduction test

Nerve conduction velocity

Definition:
Nerve conduction velocity (NCV) is a test of the speed of conduction of impulses through a nerve.

Alternative Names:
NCV

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:

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.

Normal Values:
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: 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.

Special considerations:
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.


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