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

Background: We investigated whether combining 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 radiculoneuropathy who underwent s-SCS and t-SEPs between July 2021 and December 2024. Abnormal s-SCS was defined as an amplitude <3.8 µV or a conduction velocity <39.3 m/s. Abnormal t-SEPs were defined as the failure to evoke N20, N20 latency >24.37 ms, the failure to evoke P37, or P37 latency >44.35 ms. Results: No cases showed s-SCS abnormalities with normal t-SEPs. Group 1 (G1) had normal s-SCS 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 was 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 nP37 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.