INTRODUCTION
Trans-abdominal motor evoked potential (taMEP) is a recently developed method of intraoperative neurologic monitoring for lumbo-pelvic procedures. Unlike transcranial motor evoked potential monitoring (tcMEP)/somatosensory evoked potential (SSEP), it does not require any modification of anesthetic technique, while offering the ability to perform more functional monitoring than intraoperative electromyography (EMG). Our institution has begun integrating this technique and utilizing it alongside tcMEP/SSEP and/or EMG. This report details our early experience.
METHODS
After institutional review board (IRB) approval, we retrospectively reviewed the records to date undergoing lumbo-pelvic procedures with taMEP at our center. Information collected included patient demographics, surgical indications, data from the various monitoring techniques and post operative clinical evaluation. Given the early stages of our implementation, we focus on a descriptive approach of this cohort.
RESULTS
37 cases performed by six surgeons were reviewed. 18 patients were female and 19 were male. 31 pathologies were degenerative, 4 were tumor and 2 were trauma. 21 utilized the lateral position, 15 were prone, and one was lateral and prone. All patients had EMG and taMEP monitoring. 35 had concurrent tcMEP with 17 of those 35 also having SSEP. Review of baselines showed both taMEP and tcMEP had equally reliable signals throughout the lower extremities in 11/37 cases. 12 cases noted taMEP to have a more reliable signal than tcMEP. 5 cases noted tcMEP to be more reliable than taMEP and 8 cases noted both to be unreliable. 25 patients had no reportable change in any modality throughout the procedure. One patient was noted to have unreliable signals, but a decrease was noted in the right vastus medialis amplitude on tcMEP. Of the remaining 11 patients, 2 required increased intensity in tcMEP but not taMEP voltage, 2 required increase intensity in both, 1 required increased intensity in taMEP but not tcMEP, the remainder had various changes isolated to a single muscle group. None of the previous 11 patients had any new deficit on clinical exam after surgery. There were two cases of new deficits noted after surgery. One case after lateral L4 corpectomy showed no changes in taMEP or tcMEP but the patient showed 4/5 strength in bilateral hip flexion and knee extension immediately after surgery. One case after L2-3 lateral fusion with unreliable signal in both tcMEP and taMEP noted mild decrease in hip flexor and knee extensor strength.
DISCUSSION
While it is premature to conclude whether taMEP could supplant tcMEP/SSEP, these preliminary findings are promising in implementing this technique as a supplement source of neurophysiological data for lumbo-pelvic procedures. Further research on taMEP neuromonitoring techniques is warranted.