LOSS OF INTRAOPERATIVE SOMATOSENSORY-EVOKED POTENTIALS DURING INTRAMEDULLARY SPINAL-CORD INJURY PREDICTS POSTOPERATIVE NEUROLOGIC DEFICITS IN MOTOR FUNCTION

Study Objectives: To estimate the sensitivity and specificity of somat osensory evoked potentials (SSEPs) for predicting new postoperative mo tor neurologic deficits during intramedullary spinal cord surgery; to establish whether SSEPs more accurately predicted postoperative defici ts in position and vibration sense than in strength. Design: Prospecti ve open and retrospective study. Setting: University-affiliated hospit al. Patients: 20 patients with intramedullary spinal cord tumors sched uled for surgery with intraoperative SSEPs. Interventions: Median, uln ar, and tibial nerve cortical and subcortical SSEPs were recorded cont inuously. Measurements and Main Results: Conventional intraoperative S SEP criteria considered indicative of neurologic injury were modified and defined as either the complete and permanent loss of the SSEP or t he simultaneous amplitude reduction of 50% or greater in the nearest r ecording electrode rostral to the surgical site and 0.5 millisecond in crease in the central latency. Our definition required confirmation of both amplitude and latency changes on a repeated average. All patient s had 1 or more SSEPs, which were reproducible and sufficiently stable for analysis throughout the operation. Six patients developed new pos toperative neurologic deficits. One had new motor deficits in an extre mity from which no baseline SSEPs could be elicited. In each of the ot her 5 patients, significant SSEP changes preceded the postoperative mo tor deficits in the extremity or extremities monitored. In no patient without a new postoperative motor deficit was there a significant chan ge in the SSEP. In only 2 of these 5 patients was there a documented p ostoperative loss or diminution in vibration or position sense. Conclu sions: Intraoperative SSEP changes during intramedullary spinal cord s urgery are a sensitive predictor of new postoperative motor deficits, but such changes may not correlate reliably with postoperative deficit s in position or vibration sense. In this setting SSEP monitoring serv es primarily to reassure the operating team that, when the SSEPs remai n constant, the surgery has not caused additional injury.