Improving Diagnostic Accuracy for Peripheral Neuropathy: Use of Tibial Nerve Somatosensory Evoked Potentials

Background: We investigated whether combining a sural nerve sensory conduction study (s-SCS) and tibial nerve SEPs (t-SEPs) improves diagnostic accuracy for peripheral sensory neuropathy. Methods: We retrospectively reviewed 74 consecutive cases (114 lower limbs) of patients suspected of having neuropathy or radiculopathy who underwent s-SCSs and t-SEPs between July 2021 and December 2024. Abnormal S-SCSs were defined as a reduction in amplitude or a slowing of conduction velocity. Abnormal t-SEPs were defined as failure to evoke N20 or P37, or prolonged latency of either. Results: No cases showed s-SCS abnormalities with normal t-SEPs. Then, we classified the groups based on the combination of abnormality of s-SCSs and t-SEPs. Group 1 (G1) had normal s-SCSs and normal t-SEPs, which were observed in 31 limbs (27.2%). Group 2 (G2) had normal s-SCSs and abnormal t-SEPs, which were found in 45 limbs (39.5%). Subgroups of G2 included normal N20 with abnormal P37, abnormal N20 with normal P37, and N20/P37 abnormalities. Group 3 (G3) had abnormal s-SCSs with abnormal t-SEPs, which were seen in 38 limbs (33.3%). Conclusions: Electrophysiological testing reveals normal distal and proximal sensory nerves in G1, suggesting preserved sensory nerve function. The distal sensory nerves are normal in G2. However, abnormal N20/P37 and abnormal N20 with normal P37 indicate proximal sensory nerve involvement. Normal N20 with abnormal P37 indicates posterior column dysfunction. In G3, both the distal and proximal sensory nerve segments are abnormal. Therefore, adding t-SEPs to s-SCSs allows us to evaluate the full length of the peripheral nerves, which is useful for diagnosis and assessing treatment efficacy.