Introduction: We report a novel phenomenon: suprasegmentally generated electromyographic discharges (SEDs) which can predict transcranial motor evoked potential (MEP) loss during spinal surgery at spinal cord level.
Methods: The records of 184 patients undergoing cervical (173) or thoracic (11) decompression were retrospectively reviewed. The same intramuscular recordings were used for electromyography (EMG) and MEP. Severe SEDs, seen at least two segments below the operative site, were defined as frequent, complex bursts or prolonged, repetitive (tonic) EMG discharges. At a minimum during active spinal cord decompression, MEP's were recorded after each major surgical intervention or manipulation. In the event of severe SEDs, a report of possible spinal cord impact was made and surgery paused for MEP recording.
Results: Lost MEP was observed in 15 (8.2%) cases, 7 of whom had severe SEDs prior to MEP loss. Interventions included patient re‐positioning, increased BP, instrumentation adjustment, wake‐up test, or surgical pause. MEP recovered in 10 cases; 5 patients lost MEP without recovery and with worsened post‐operative neurological examination (2.7% true positive). Severe SEDs were seen in a total of 15 cases and anticipated MEP loss in 7/15. In 13/15 cases, manipulations near dura were the proximate cause of severe SED's. The positive predictive value of severe SED occurrence for MEP loss was 0.47; the negative predictive value of severe SED absence for MEP preservation was 0.95.
Conclusion: When severe SEDs are identified during active spinal cord decompression, the risk of MEP loss approaches 50%. If severe SEDs are observed, spinal cord impact may have occurred. At a minimum, surgical pause and MEP performance are recommended.
Significance: We report a novel diagnostic phenomenon: suprasegmentally generated electromyographic discharges (SEDs) which can predict transcranial motor evoked potential (MEP) loss during spinal surgery at spinal cord level and help avoid further spinal cord insult during surgery