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December 1984

Averaging Techniques to Define the Low-Amplitude Compound Motor Action Potential

Author Affiliations

From the Department of Neurology, University of Arizona, Tucson.

Arch Neurol. 1984;41(12):1307. doi:10.1001/archneur.1984.04050230097032

Most physicians are aware of the dramatic advances that have occurred in the past decade in regard to the clinical application of the averaged evoked potential. Virtually all electrodiagnosticians have been equally well aware of the ability of the digital averager to extract the low-amplitude sensory nerve action potential from a potpourri of electromyographic (EMG), ECG, movement, and extraneous electromagnetic artifact. In practice, few electrodiagnosticians use the averager to define better the very low-amplitude compound motor action potential as is seen in the foot and hand muscles in various peripheral neuropathies.

In general, the distal latency can be reliably measured in these situations. The proximal latency may be ill defined because the electrokinetic and, to a lesser extent, volume-conducted EMG activity generated by the contraction of the better preserved proximal muscles may exceed the amplitude of the evoked compound motor action potential. It may also precede it, resulting in a

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