Evaluation of Side-to-Side Differences in Lower Extremity Sensory Nerve Action Potential (SNAP) Amplitude in Relation...

Anatomical variations and technical factors can lead to side-to-side differences in nerve conduction studies, potentially causing false positive diagnoses. This study aimed to define normal limits of side-to-side differences in sural and superficial peroneal (SP) sensory nerve action potential (SNAP) amplitudes, considering their association with lower extremity motor nerves.

Fifty healthy adults were assessed for lower extremity compound muscle action potential (CMAP) and SNAP amplitudes. The upper limit of side-to-side differences was defined as the mean plus two standard deviations. Associations between CMAP and SNAP amplitudes, based on motor-sensory nerve relationships, were analyzed using Pearson correlation and linear regression. CMAP amplitude differences were used as the references.

Significant positive correlations were found between left peroneal CMAP and sural SNAP (r=0.451, p=0.001), and between right peroneal CMAP and SP SNAP (r=0.304, p=0.032). Peroneal CMAP amplitude significantly affected left sural and right SP SNAP amplitudes (B=1.246, p=0.001; B=0.672, p=0.032). If the peroneal CMAP side-to-side difference is ≤4.04 mV, sural and SP SNAP differences up to 7.76 and 6.7 µV, respectively, may be considered normal.

Considering peroneal CMAP amplitude asymmetry may help improve the interpretation of lower extremity SNAP differences and reduce the risk of false positives.