# Evaluation of Side-to-Side Differences in Lower Extremity Sensory Nerve Action Potential (SNAP) Amplitude in Relation to Motor Nerve Conduction Studies

## TL;DR

This study defines normal side-to-side differences in sensory nerve amplitudes to avoid false positive nerve diagnoses.

## Contribution

The study establishes normal limits for sensory nerve action potential differences in relation to motor nerve conduction.

## Key findings

- Left peroneal CMAP correlates with sural SNAP (r=0.451, p=0.001).
- Peroneal CMAP differences up to 4.04 mV may allow sural and SP SNAP differences up to 7.76 and 6.7 µV as normal.

## Abstract

Introduction and aim: 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.

Methods: 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.

Results: 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.

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