Anterior spinal cord injury with preserved neurogenic 'motor' evoked potentials

Objective: To describe two cases in which intraoperative monitoring of neur ogenic 'motor' evoked potentials (NMEPs) did not identify a spinal cord inj ury that resulted in paraplegia. Methods: Bilateral tibial nerve somatosensory evoked potential (SEP) and NM EP testing was performed in two patients during spinal deformity corrective surgery using standard stimulation and recording parameters. These potenti als were obtained repetitively throughout the primary procedures and were p erformed again during a subsequent procedure that took place after the disc overy of paraplegia. Results. SEP and NMEP signals were preserved in both patients and no advers e events were identified during the initial procedures. Postoperatively, pa raplegia was identified immediately upon recovery from anesthesia and prese rved posterior column function was apparent on clinical exam. In the proced ures following the discovery of paraplegia, SEP and NMEP signals remained c omparable with signals elicited in the initial sur-aeries. Conclusions: Based on these cases and previously published experimental evi dence, we conclude that while 'NMEPs' remain a useful second test of spinal cord function, they are not reliable indicators of motor tract function. A n alternate term, such as 'spinally-elicited peripheral nerve responses' sh ould be used. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.