A prospective comparison of neurogenic mixed evoked potential stimulation methods - Utility of epidural elicitation during posterior spinal surgery

Study Design. A prospective study of 50 patients who underwent posterior th oracic or thoracolumbar instrumented spinal surgery from June 1998 through June Objectives. To highlight the advantages and disadvantages of of neurogenic mixed evoked potential (NMEP) data obtained with three methods of stimulati on: epidural, spinous process, and percutaneous. Summary of Background Data. Reports in the literature have established the efficacy of epidural, spinous excess,and percutaneous stimulation of the NM EP response. The three methods have not been compared for reliability, sens itivity, and specificity. Methods. The study group consisted of 50 patients who underwent posterior t horacic or thoracolumbar instrumented spinal surgery from June 1998 through June 1999. Somatosensory-evoked potentials were used to monitor upper and lower extremities, An attempt to obtain NMEPs was made in all patients by u sing percutaneous (PERC-NMEP), spinous process (SP-NMEP), and epidural (EPI -NMEP) stimulation. These data were evaluated for reliability, sensitivity, and specificity. The number of minutes monitored in the postcorrection per iod were calculated for each method, and stimulus intensities were Results. In the current study, PERC-NMEPs were obtained in 88% of the patie nts and were maintained in 91% of those: cases, SP-NMEPs were obtained in 9 6% and maintained In 77%, and EPI-NMEPs were obtained in 100% and maintaine d in 88%. Data collection continued in the postcorrection period for 46 min utes for PERC-NMEPS, 19 minutes for SP-NMEPs, and 23 minutes for EPI-NMEPs. The study group had no true-positive or false-negative findings. Conclusions. Results showed that EPI-NMEPs provide reliable data in a great er number of patients than either SP-NMEPs or PERC-NMEPs. However, PERC-NME P data are readily maintained during and after the critical time window aft er corrective spinal maneuvers. The NMEPs elicited with both percutaneous a nd epidural stimulation have a useful role in an intraoperative spinal cord -monitoring protocol.