title: Changes in transcranial motor evoked potentials during intramedullary spinal cord tumor resection correlate with postoperative motor function.
abstract: OBJECTIVE
  Intraoperative monitoring of transcranial motor evoked potentials (TcMEPs) has been investigated recently as a means of preventing motor deficits associated with resection of intramedullary spinal cord tumors (IMSCTs). In this study, we hypothesized that changes in the intraoperative MEPs during tumor resection correlate with postoperative motor function deficits.
  
  
  METHODS
  A retrospective record review was conducted for 28 patients who underwent resection of an IMSCT using myogenic or muscle-recorded TcMEPs during a 44-month period. Intraoperative MEP recordings and results from preoperative, immediate postoperative, and subsequent follow-up neurological examinations were analyzed.
  
  
  RESULTS
  Of the 28 patients who underwent resection of an IMSCT using TcMEPs, MEP changes occurred in 13 patients (46%). Impaired motor conduction was detected by changes in pattern and duration of the MEP waveform morphology (polyphasic to biphasic in 9 patients and polyphasic to biphasic to loss of MEP response in 5 patients, 1 patient demonstrated both changes) and by an increase in voltage threshold (median, 175 V; range, 100-225 V; n = 22 extremities). Alterations in morphology and reduction in duration of the MEP response persisted despite significant increases in stimulation voltage. In 12 patients, reductions in the complexity and/or loss of the TcMEP waveform correlated with motor grade loss in the immediate postoperative period (P < 0.0001), at discharge (P < 0.001), and at follow-up (P < 0.001). The decrease in the duration of the response correlated with motor grade loss immediately after surgery (P < 0.001), at discharge (P < 0.0001), and at follow-up (P < 0.005).
  
  
  CONCLUSIONS
  These results support the application of distal muscle-recorded TcMEPs to predict the occurrence and severity of postoperative motor deficits during resection of IMSCTs. Attention to such quantitative intraoperative monitoring data may help to minimize postoperative motor deficits by avoiding or correcting excessive spinal cord manipulation and modifying surgical technique during tumor resection.
authors.affiliation: Department of Neurological Surgery, University of California, San Francisco, San Francisco, California 94143-0112, USA. quinones@post.harvard.edu
authors.forename: Alfredo
authors.initials: A
authors.lastname: Quiñones-Hinojosa
authors.forename: Russ
authors.initials: R
authors.lastname: Lyon
authors.forename: Gabriel
authors.initials: G
authors.lastname: Zada
authors.forename: Kathleen R
authors.initials: KR
authors.lastname: Lamborn
authors.forename: Nalin
authors.initials: N
authors.lastname: Gupta
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Parsa
authors.forename: Michael W
authors.initials: MW
authors.lastname: McDermott
authors.forename: Philip R
authors.initials: PR
authors.lastname: Weinstein
mesh_terms: D000328:Adult; D001921:Brain / Q000503:physiopathology*; D020295:Brain Stem Neoplasms / Q000532:radiotherapy / Q000534:rehabilitation / Q000601:surgery*; D003131:Combined Modality Therapy; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007902:Length of Stay; D008297:Male; D016343:Monitoring, Intraoperative; D009043:Motor Activity / Q000502:physiology*; D012189:Retrospective Studies; D013120:Spinal Cord Neoplasms / Q000532:radiotherapy / Q000534:rehabilitation / Q000601:surgery*