Loss of somatosensory evoked potentials during intramedullary spinal cord surgery predicts postoperative neurologic deficits in motor function [corrected].
OBJECTIVE
To estimate the sensitivity and specificity of somatosensory evoked potentials (SSEPs) for predicting new postoperative motor neurologic deficits during intramedullary spinal cord surgery; to establish whether SSEPs more accurately predicted postoperative deficits in position and vibration sense than in strength.


METHODS
Prospective open and retrospective study.


METHODS
University-affiliated hospital.


METHODS
20 patients with intramedullary spinal cord tumors scheduled for surgery with intraoperative SSEPs.


METHODS
Median, ulnar, and tibial nerve cortical and subcortical SSEPs were recorded continuously.


RESULTS
Conventional intraoperative SSEP criteria considered indicative of neurologic injury were modified and defined as either the complete and permanent loss of the SSEP or the simultaneous amplitude reduction of 50% or greater in the nearest recording electrode rostral to the surgical site and 0.5 millisecond increase in the central latency. Our definition required confirmation of both amplitude and latency changes on a repeated average. All patients had 1 or more SSEPs, which were reproducible and sufficiently stable for analysis throughout the operation. Six patients developed new postoperative neurologic deficits. One had new motor deficits in an extremity from which no baseline SSEPs could be elicited. In each of the other 5 patients, significant SSEP changes preceded the postoperative motor deficits in the extremity or extremities monitored. In no patient without a new postoperative motor deficit was there a significant change in the SSEP. In only 2 of these 5 patients was there a documented postoperative loss or diminution in vibration or position sense.


CONCLUSIONS
Intraoperative SSEP changes during intramedullary spinal cord surgery are a sensitive predictor of new postoperative motor deficits, but such changes may not correlate reliably with postoperative deficits in position or vibration sense. In this setting SSEP monitoring serves primarily to reassure the operating team that, when the SSEPs remain constant, the surgery has not caused additional injury.
Kearse
L A
LA
Department of Anesthesia, Massachusetts General Hospital, Boston 02114.
Lopez-Bresnahan
M
M
McPeck
K
K
Tambe
V
V
D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D007432:Intraoperative Period; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons; D009422:Nervous System Diseases; D011183:Postoperative Complications; D011446:Prospective Studies; D012189:Retrospective Studies; D013120:Spinal Cord Neoplasms / Q000503:physiopathology / Q000601:surgery*