Fibular motor nerve conduction studies: Investigating the mechanism for compound muscle action potential amplitude drop with proximal stimulation

Abstract

Introduction: The compound muscle action potential (CMAP) amplitude of extensor digitorum brevis can show a drop with proximal stimulation in normal fibular nerves. Methods: We assessed the contribution of the far-field potential recorded by the reference electrode (R-CMAP) to the fibular CMAP. Negative R-CMAP amplitude, peak-to-peak amplitude, and negative area were measured and correlated with the amplitude decrease. Fibular motor nerves from 14 healthy participants were studied. Results: The mean CMAP amplitude drop with proximal stimulation was 14.0±9.3%, including a >30% reduction in 1 study. All measured R-CMAP parameters correlated with the degree of amplitude drop. Conclusions: A gre..