Sacral Dermatomal Somatosensory Evoked Potentials Its Techniques and Clinical Significance

ABSTRACT

Pudendal nerve somatosensory evoked potential (PSEP) study has been utilized for the evaluation of neurogenic dysfunctions of bowel, bladder and sex. However, the reluctance of sexual organ exposure during the study can be a serions limiting factor. Sacral dermatomal somatosensory evoked potential (SDSEP) study stimulating sacral dermatome can be an alternative or a supportive method for the PSEP study. The purpose of this study is to present the techniques, normal values and clinical significance of SDSEP study in spinal cord injured patients. Thirty control subjects and thirty-five spinal cord injured patients were enrolled for the study. Using ring electrodes, S3 dermatome was stimulated by Nicolet Viking IV EMG/EP system. Evoked responses were recorded at the cortex(Cz'-Fz) by the needle electrodes. The latencies and amplitudes of SDSEP and PSEP responses were obtained and analyzed. In control subjects, the P1 latencies of SDSEP were 34.72+/-2.68 msec for the right and 33.54+/-1.95 msec for the left. The N1 latencies were 43.06+/-2.31 msec for the right and 42.14+/-2.29 msec for the left, respectively. The P1N1 amplitudes of control subjects were 0.73+/-0.40 V for the right and 0.69+/-0.22 V for the left. The coincidence of SDSEP and PSEP was 86.7% of the spinal cord injured patients. In conclusion, SDSEP study could be used for the evaluation of neurogenic dysfunctions of bladder, bowel, and sex in conjunction with the PSEP study.