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© Dirk Biddle
A Nerve Conduction Velocity (NCV or nerve conduction study) test measures how quickly electrical impulses move along a nerve. Nerves with damaged myelin transmit signals slower than undamaged nerve cells, while nerves with destroyed axons cannot transmit signals at all. Most neuropathies are caused by damage to the nerve's axon rather than damage to the myelin sheath surrounding the nerve. The nerve conduction velocity test is used to distinguish between true nerve disorders (such as Charcot-Marie-Tooth disease) and conditions where muscles are affected by nerve injury (such as in the vasculitides).
During the test, flat electrodes are placed on the patient's skin, at intervals, above the nerve to be examined for damage. One of the electrodes stimulates the nerve by transmitting a very weak electrical impulse through it. The impulse may feel a little like an electric shock, and depending on how strong it is, it will be felt by the patient in varying degrees and may be uncomfortable for some patients. The test carries no risk of electrical shock. The other electrodes pick up and measure the strength of the impulse that reaches them. The conduction velocity of the nerve is calculated from the distance between the electrodes and the time it takes for the impulse to move between them. The speed of transmission is related to the diameter of the nerve and its myelination. The result is therefore compared with the speed of transmission of an undamaged nerve.
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 uraemia (from kidney failure), Traumatic injury to a nerve, Guillain-Barre syndrome, Diphtheria, 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 and Ulnar nerve dysfunction (1).
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1)http://www.nlm.nih.gov/medlineplus/ency/article/003927.htm
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