Abstract
Two methods can be used to evaluate the results of intraoperative motor-evoked potential (MEP) monitoring: evaluation of amplitude and evaluation of the threshold stimulation intensity. We have been using the former approach. The normalization of MEP after transcranial stimulation (TCMEP) by compound muscle action potential (CMAP) after peripheral nerve stimulation has been reported. In this study, we evaluated the efficacy of such CMAP normalization in TCMEP. Since March 2003, TCMEP monitoring with CMAP normalization was performed during 436 neurosurgical operations. In 91 aneurysmal operations, a difference in sensitivity between with and without CMAP normalization was recorded. In 37 brain tumor operations, TCMEP could be used to support MEP by direct cortical stimulation because of the low sensitivity of TCMEP. In 245 spinal operations, CMAP normalization was not shown to significantly prevent postoperative motor palsy. In 202 operations for compressive spinal or spinal nerve disease, the mean relative amplitude rate after CMAP normalization of the most affected muscle in the group with excellent postoperative results (recovery rate according to the Japan Orthopedic Association score was more than 50%) was significantly higher than that in other groups (p=0.0224). All patients with an increase in amplitude with CMAP normalization of more than 20% achieved neurological recovery postoperatively. These results suggest that postoperative neurological recovery after spinal operation for compressive spinal or spinal nerve disease could be predicted by CMAP normalization.
