title: Intraoperative Motor-Evoked Potential Disappearance versus Amplitude-Decrement Alarm Criteria During Cervical Spinal Surgery: A Long-Term Prognosis.
abstract: OBJECTIVE
  We studied the clinical significance of amplitude-reduction and disappearance alarm criteria for transcranial electric muscle motor-evoked potentials (MEPs) during cervical spinal surgery according to different lesion locations [intramedullary (IM) vs. nonintramedullary (NIM)] by evaluating the long-term postoperative motor status.
  
  
  METHODS
  In total, 723 patients were retrospectively dichotomized into the IM and NIM groups. Each limb was analyzed respectively. One hundred and sixteen limbs from 30 patients with IM tumors and 2,761 limbs from 693 patients without IM tumors were enrolled. Postoperative motor deficits were assessed up to 6 months after surgery.
  
  
  RESULTS
  At the end of surgery, 61 limbs (2.2%) in the NIM group and 14 limbs (12.1%) in the IM group showed MEP amplitudes that had decreased to below 50% of baseline, with 13 of the NIM limbs (21.3%) and 2 of the IM limbs (14.3%) showing MEP disappearance. Thirteen NIM limbs (0.5%) and 5 IM limbs (4.3%) showed postoperative motor deficits. The criterion for disappearance showed a lower sensitivity for the immediate motor deficit than did the criterion for amplitude decrement in both the IM and NIM groups. However, the disappearance criterion showed the same sensitivity as the 70%-decrement criterion in IM (100%) and NIM (83%) surgeries for the motor deficit at 6 months after surgery. Moreover, it has the highest specificity for the motor deficits among diverse alarm criteria, from 24 hours to 6 months after surgery, in both the IM and NIM groups.
  
  
  CONCLUSIONS
  The MEP disappearance alarm criterion had a high specificity in predicting the long-term prognosis after cervical spinal surgery. However, because it can have a low sensitivity in predicting an immediate postoperative deficit, combining different MEP alarm criteria according to the aim of specific instances of cervical spinal surgery is likely to be useful in practical intraoperative monitoring.
authors.affiliation: Department of Neurology, Myung Diagnostic Radiology Clinic, Seoul, Korea.
authors.forename: Dong Gun
authors.initials: DG
authors.lastname: Kim
authors.affiliation: Department of Neurosurgery, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Young Doo
authors.initials: YD
authors.lastname: Choi
authors.affiliation: Department of Neurosurgery, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Seung Hyun
authors.initials: SH
authors.lastname: Jin
authors.affiliation: Department of Neurosurgery, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Chi Heon
authors.initials: CH
authors.lastname: Kim
authors.affiliation: Department of Neurology, Gachon University Gil Medical Center, Inchon, Korea.
authors.forename: Kwang Woo
authors.initials: KW
authors.lastname: Lee
authors.affiliation: Department of Neurology, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Kyung Seok
authors.initials: KS
authors.lastname: Park
authors.affiliation: Department of Neurosurgery, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea. chungc@snu.ac.kr.
authors.forename: Chun Kee
authors.initials: CK
authors.lastname: Chung
authors.affiliation: Department of Neurology, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea. sueh916@gmail.com.
authors.forename: Sung Min
authors.initials: SM
authors.lastname: Kim
keywords: alarm criteria; cervical spinal surgery; intraoperative monitoring; long-term prognosis; motor deficit; motor-evoked potential