Motor evoked potential monitoring during upper cervical spine surgery.

Motor evoked potential (MEP) produced by transcranial electrical stimulation was recorded from an epidural electrode in 20 consecutive patients during upper cervical spine surgery. In 5 patients, transient attenuation to approximately 50% followed by complete recovery was observed, and no neurologic deficit was noted. One patient had complete loss of MEP and was left a respiratory quadriplegic. In 2 cases, MEP amplitudes increased after tumor extirpation and remarkable remissions were observed. The MEP correlated with clinical outcomes and was a useful monitoring technique for upper cervical spine surgery, free of complication. In cat experiments designed to analyze conducting pathways, the maximal amplitude of the initial spike of MEP existed in the ventromedial spinal cord, which contains the extrapyramidal tracts. Motor evoked potential was proven to reflect motor function based on the spinal cord compression study.