Nerve conduction studies: Basic concepts

Nerve conduction studies (NCSs) are an essential tool in the evaluation of the peripheral nervous system. The sensory nerve action potential (SNAP) provides information on the sensory nerve axon and its pathway from the distal receptors in the skin to the dorsal root ganglia, while the compound muscle action potential (CMAP) is an assessment of the motor nerve fibers from their origins in the anterior horn cell to their termination along muscle fibers. Various parameters of the SNAP and CMAP waveforms are used to determine the number of functioning nerve fibers and the speed of conduction. Similarly, specific electrodiagnostic patterns involving SNAP and CMAP amplitudes, latencies and other measurements can help discern the underlying nerve pathophysiology as either axon loss or demyelinating in nature. Numerous technical and environmental factors can affect the NCS and should be recognized and corrected if possible. Finally, while basic NCSs are a noninvasive and low-risk procedure, safety issues for patients with implanted electrical devices should be considered.