Motor evoked potential monitoring improves outcome after surgery for intramedullary spinal cord tumors: a historical control study

Abstract

Objective: The value of intraoperative neurophysiological monitoring (INM) during intramedullary spinal cord tumor surgery remains debated. This historical control study tests the hypothesis that INM monitoring improves neurological outcome.

Methods: In 50 patients operated on after September 2000, we monitored somatosensory evoked potentials and transcranially elicited epidural (D-wave) and muscle motor evoked potentials (INM group). The historical control group consisted of 50 patients selected from among 301 patients who underwent intramedullary spinal cord tumor surgery, previously operated on by the same team without INM. Matching by preoperative neurological status (McCormick scale), histological findings, tumor location, and extent of removal were blind to outcome. A more than 50% somatosensory evoked potential amplitude decrement influenced only myelotomy. Muscle motor evoked potential disappearance modified surgery, but more than 50% D-wave amplitude decrement was the major indication to stop surgery. The postoperative to preoperative McCormick grade variation at discharge and at a follow-up of at least 3 months was compared between the two groups (Student's t tests).

Results: Follow-up McCormick grade variation in the INM group (mean, +0.28) was significantly better (P = 0.0016) than that of the historical control group (mean, -0.16). At discharge, there was a trend (P = 0.1224) toward better McCormick grade variation in the INM group (mean, -0.26) than in the historical control group (mean, -0.5).

Conclusion: The applied motor evoked potential methods seem to improve long-term motor outcome significantly. Early motor outcome is similar because of transient motor deficits in the INM group, which can be predicted at the end of surgery by the neurophysiological profile of patients.