S2, S3, and S4 Sacral Dermatomal Evoked Potentials: Technical Parameters and Normative Values.

Purpose: The existing literature on the sacral dermatomal evoked potentials (dSEPs) is limited. This study aims to develop stimulating parameters and establish normative values for S2, S3, and S4 sacral dermatomes in healthy adult populations.

Methods: Twenty healthy adult volunteers were enrolled in the study. The study was ethically approved, and written consent for participation was provided. All participants underwent tibial, pudendal, S2, S3, and S4 dSEPs. Stimulating and recorded parameters were established for all evoked potentials. P40 latency, amplitude, and interpeak parameters were calculated for each waveform. A comparison was made between tibial, pudendal somatosensory evoked potentials, and all sacral dSEPs. Normative values were generated for sacral dSEPs based on various height, age, and Body Mass Index (BMI) parameters.

Results: The sacral dSEPs were well tolerated and recorded in all participants. S2 latency was mildly influenced by age and height, while S3 and S4 latencies were unaffected by age or height. BMI does not affect the S2 and S3 latencies but mildly affects the S4 latency. Sacral dSEP latencies were comparable with pudendal SEPS but not with the tibial somatosensory evoked potential.

Conclusions: The S2, S3, and S4 sacral dSEPs can be used as diagnostic tools to evaluate sacral nerve lesions such as cauda equina syndrome and Tarlov cysts, complementary to pudendal and tibial somatosensory evoked potentials.