What are nerve conduction studies?

Updated: Aug 20, 2018
  • Author: Stephen Kishner, MD, MHA; Chief Editor: Jonathan P Miller, MD  more...
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Answer

For this test, a series of surface electrodes are placed at different locations along specific peripheral nerves. The nerve is stimulated at one site and recorded at a different site to determine if the nerve is conducting electrical impulses appropriately.

Each electrical stimulation is recorded as a waveform on a computer and analyzed by the electromyographer performing the test. [2]

Standard nerve conduction studies typically include motor nerve conduction, sensory nerve conduction, F waves, and H reflexes.

Sensory and motor nerve conduction studies involve analysis of specific parameters, including latency, conduction velocity, and amplitude. Onset latency is the time it takes for the stimulus to initiate an evoked potential and reflects the conduction along the fastest fibers. Peak latency is the latency along the majority of axons and is measured at the peak amplitude. [3] Both are affected by the state of the myelination of the nerve.

The conduction velocity along the nerve also depends on the state of myelination and is often decreased in disorders or trauma that affects nerve myelination, although it may be normal if a few myelinated axons remain intact. Reduction of amplitude of recorded responses generally indicates a loss of axons. [4]

These studies, in conjunction with the physical examination and correlation to a set of normative values, assist the electromyographer in diagnosing a multitude of nerve disorders, including entrapment neuropathies, brachial plexopathies, and polyneuropathies.

It is often important to distinguish between sensory and motor nerves, as certain disease processes can affect one or both. Radiculopathy produces motor deficits but does not affect sensory nerves since the anatomic location of the damage is proximal to the dorsal root ganglion. When a lesion is distal to the dorsal root ganglion, such as in brachial plexopathies, both motor and sensory nerves are affected.


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