Nerve Conduction Testing
Last updated: October 10, 2014
Synonyms: Nerve conduction velocity, latency studies.
Definition: Evaluation of peripheral nerves by nerve conduction testing involves measurement of the velocity of an electrical stimulus in a target nerve.
Method: The test is done by percutaneous stimulation of a nerve at two separate points along its course and recording the electrical response (evoked action potentials) on the skin (for sensory nerves) or an associated muscle (for motor nerves). This test helps to evaluate both generalized and localized neuropathies that might affect peripheral nerves or muscle function. Nerve conduction testing is usually performed by a specially trained physiatrist or neurologist, often at the same time as electromyography. Referrals should include a clinical history and the reason for the procedure.
Normal in: Nerve conduction is normal in primary muscle disorders, myasthenia gravis radiculopathies, and amyotrophic lateral sclerosis.
Abnormal in: Detection of abnormalities in all extremities suggests generalized disorders such as polyneuropathy, mononeuritis multiplex, or Guillain-Barré syndrome. If only localized abnormalities are found, then mechanical problems with nerve entrapment (e.g., carpal tunnel syndrome) or localized inflammatory problems such as mononeuritis multiplex should be considered. Measurements to confirm a diagnosis of carpal or tarsal tunnel syndrome can be limited to the involved extremity, whereas a more generalized problem requires evaluation of all limbs.
Confounding Factors: A cardiac pacemaker (or implanted defibrillator) may influence evoked potentials. Results are unreliable or unobtainable in agitated or uncooperative patients. Results are not affected by medications.
Indications: Nerve conduction velocity testing is a noninvasive procedure appropriate for evaluating peripheral neuropathies. Specifically, nerve conduction velocity is useful in determining the extent of nerve involvement (i.e., polyneuropathy versus mononeuritis multiplex) and whether a demyelinating or axonal process is present. It is often useful in distinguishing neuropathic from myopathic causes of muscle weakness. Diagnostic findings may occur in patients with entrapment syndromes (e.g., carpal tunnel syndrome), Guillain- Barré syndrome, Eaton-Lambert syndrome, and myasthenia gravis.
Cost: $200–500 per limb (cost includes evaluation by the neurologist or physiatrist).