Tibial motor and sural electrophysiological relationship in subjects without and patients with mild axonal peripheral neuropathy

The distal motor fibers of the tibial and sural nerves are predominantly derived from the S1 root. We aimed to describe the electrophysiological relationship of these two nerves. Clinical, radiological and neurophysiological data of patients with mild, length-dependent, peripheral neuropathy (PN) and subjects without PN were retrospectively collected and analyzed. Eighty-eight individuals without PN and 24 patients with mild axonal PN who had no evidence of lumbosacral radiculopathy were included for analysis. Significant positive correlations were observed for the tibial CMAP and the sural SNAP for both controls and patients. Multivariate linear regression analyses showed that the predicted tibial CMAP can be calculated using the following equations: for male subjects without PN, tibial CMAP = 20.7 − 0.21 × age; for female subjects without PN, tibial CMAP = 23.3 − 0.21 × age and for patients with mild PN, tibial CMAP = 2.7 + sural SNAP. This study demonstrates the high correlation between the tibial CMAP and the sural SNAP in subjects without PN and patients with mild axonal peripheral neuropathy, and provides mathematical equations for the calculation of the predicted tibial CMAP for such individuals.