• Sho Kobayashi, Yukihiro Matsuyama, Kenichi Shinomiya, Shigenori Kawabata, Muneharu Ando, Tsukasa Kanchiku, Takanori Saito, Masahito Takahashi, Zenya Ito, Akio Muramoto, Yasushi Fujiwara, Kazunobu Kida, Kei Yamada, Kanichiro Wada, Naoya Yamamoto, Kazuhiko Satomi, and Toshikazu Tani.
• Department of Orthopedic Surgery, Hamamatsu University School of Medicine, Hamamatsu;
• J Neurosurg Spine. 2014 Jan 1; 20 (1): 102-7.

ObjectAlthough multimodal intraoperative spinal cord monitoring provides greater accuracy, transcranial electrical stimulation motor evoked potential (TcMEP) monitoring became the gold standard for intraoperative spinal cord monitoring. However, there is no definite alarm point for TcMEPs because a multicenter study is lacking. Thus, based on their experience with 48 true-positive cases (that is, a decrease in potentials followed by a new neurological motor deficit postoperatively) encountered between 2007 and 2009, the authors set a 70% decrease in amplitude as the alarm point for TcMEPs.MethodsA total of 959 cases of spinal deformity, spinal cord tumor, and ossification of the posterior longitudinal ligament (OPLL) treated between 2010 and 2012 are included in this prospective multicenter study (18 institutions). These institutions are part of the Japanese Society for Spine Surgery and Related Research monitoring working group and the study group on spinal ligament ossification. The authors prospectively analyzed TcMEP variability and pre- and postoperative motor deficits. A 70% decrease in amplitude was designated as the alarm point.ResultsThere were only 2 false-negative cases, which occurred during surgery for intramedullary spinal cord tumors. This new alarm criterion provided high sensitivity (95%) and specificity (91%) for intraoperative spinal cord monitoring and favorable accuracy, except in cases of intramedullary spinal cord tumor.ConclusionsThis study is the first prospective multicenter study to investigate the alarm point of TcMEPs. The authors recommend the designation of an alarm point of a 70% decrease in amplitude for routine spinal cord monitoring, particularly during surgery for spinal deformity, OPLL, and extramedullary spinal cord tumor.

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