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In Reply: Guidelines for the Use of Electrophysiological Monitoring for Surgery of the Human Spinal Column and Spinal Cord

In Reply: Guidelines for the Use of Electrophysiological Monitoring for Surgery of the Human... To the Editor: The authors of the Guidelines for the Use of Electrophysiological Monitoring for Surgery of the Human Spinal Column and Spinal Cord1 are pleased to respond to the letter to the editor regarding this work.2 To begin, it is important to point out that our work was a guideline based upon a systematic review of the literature, and not a meta-analysis. The standards for reporting of guidelines, systematic reviews, and meta-analyses are all quite different and those demanded by the American Association of Neurological Surgeons and the Congress of Neurological Surgeons for guidelines were followed in this publication. We are happy to respond to the points made by the authors of the letter,2 as will be seen below. In 2017, Harel et al3 reported their experience with resection of intradural extramedullary spinal tumors with and without the use of intraoperative electrophysiological monitoring (IOM). Their retrospective, historically controlled study compared 41 patients who underwent tumor resection with the use of IOM with 70 patients who underwent tumor resection without the use of IOM. The authors attempt to evaluate IOM as both a diagnostic tool and a therapeutic adjunct in accordance with a validated medical evidence rating scheme.4 The Bayesian analysis of monitoring alerts and retrospective nature of the study earn a class II medical evidence rating for the use of IOM as a diagnostic tool. Evaluation of postoperative neurological deficit rates in a retrospective, comparative manner (not significant between the 2 groups) earns a class II medical evidence rating for the use of IOM as a therapeutic adjunct. Despite their laudable efforts, the authors admit several study limitations, among them a significantly different rate of instrumentation (0% in the historical control group and 17% in the study group). We agree that this study group discordance is unfortunate, and it does not alter our recommendations. A weak, negative result does not support an argument for therapeutic efficacy. In 2014, Choi et al5 retrospectively evaluated the use of IOM as a therapeutic adjunct in 76 patients who underwent resection of intramedullary spinal cord tumors. Fifty patients who underwent resection with the use of IOM were compared to 26 patients who underwent resection without IOM with respect to rate of gross total tumor resection and neurological outcome. Despite a promising result from the initial, univariate analysis, the authors appropriately conducted a more comprehensive, multivariate analysis to account for numerous patient factors. In their final model, the use of IOM did not result in a statistically significant effect on either rate of gross total tumor resection or neurological outcome. While we agree that sample size and heterogeneity may have influenced the statistical outcomes of this class II medical evidence study, we can only evaluate the study and its results as designed/reported. In the context of a medical evidence-based guidelines document, it is scientifically inappropriate to speculate on how these results might have changed were the study designed differently. The study by Tamkus et al6 was published after submission of the Guidelines for the Use of Electrophysiological Monitoring for Surgery of the Human Spinal Column and Spinal Cord1 and was not included in our published analysis. The authors present an industry-sponsored (Nuvasive Inc, San Diego, California), observational, noncomparative review of patients who underwent spinal column or spinal cord surgery with the use of IOM and were found to have a new or worse postoperative neurological deficit. The relationship of the surgeon's decision to intervene (or not), as well as the nature of that intervention, was compared with respect to rate of improvement in neurological deficit at time of discharge. Industry sponsorship notwithstanding, this study is plagued by numerous statistical and methodological issues and represents class III medical evidence study (at best). The authors provide no baseline demographic statistics for the “intervention” and “no intervention group.” An enormous variety of spinal pathologies encompassing all spinal segments (including lumbosacral) were analyzed in aggregate. No objective measure of baseline or postoperative neurological function (eg, Japanese Orthopaedic Association, McCormick grade, Benzel grade, etc7) was presented. No follow-up data were obtained beyond hospital discharge. All data points were gleaned from IOM technologists’ proprietary records (not from electronic medical records). We agree with the authors that this “study also cannot determine the impact of Intraoperative Neuromonitoring in improving outcomes by preventing postoperative neurologic deficits… [and that] the assumption that there is a causal link between a failure to intervene and a poor outcome may be flawed.” Unfortunately, this study fails to appropriately evaluate IOM as either a diagnostic tool or a therapeutic adjunct. For these reasons, inclusion of this article would not alter our recommendations for the use of IOM in either a diagnostic or therapeutic capacity. Lastly, the difficulty that the authors of the letter2 have in understanding the differences between diagnostic and therapeutic usefulness of IOM shows a lack of understanding of the 2 aspects of tools such as this. IOM is well able to show that an injury has/might have occurred (ie, can make the diagnosis), but it has not been demonstrated that the indications of change in neurological status then lead to surgical (or other) responses that provide for an improved outcome (ie, therapeutic benefit) for spinal surgery patients. In fact, it may not be clear to the team what, if any, maneuver caused the changes, or what, if any, intervention might change the outcome. Their ideas about checklists to improve communication between team members in the operating room are interesting, but well beyond the scope of our guidelines, and do not address the issue of apparent dissociation between diagnosis and therapy. However, we would certainly encourage the authors of the letter to assess whether implementation of such a checklist would produce some evidence that could be used to support (or not) the use of IOM as a therapeutic adjunct in spinal surgery. So far, those data are missing from the literature. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Hadley MN, Shank CD, Rozzelle CJ, Walters BC. Guidelines for the use of electrophysiological monitoring for surgery of the human spinal column and spinal cord. Neurosurgery . 2017; 81( 5): 713- 732. Google Scholar PubMed  2. Wilkinson M, Houlden D. Letter: guidelines for the use of electrophysiologial monitoring for surgery of the human spinal column and spinal cord. Neurosurgery . 2018. doi: 10.1093/neuros/nyy157. 3. Harel R, Schleifer D, Appel S, Attia M, Cohen ZR, Knoller N. Spinal intradural extramedullary tumors: the value of intraoperative neurophysiologic monitoring on surgical outcome. Neurosurg Rev . 2017; 40( 4): 613- 619. Google Scholar CrossRef Search ADS PubMed  4. Walters BC. Methodology of the guidelines for the management of acute cervical spine and spinal cord injuries. Neurosurgery . 2013; 72( suppl 2): 17- 21. Google Scholar CrossRef Search ADS PubMed  5. Choi I, Hyun SJ, Kang JK, Rhim SC. Combined muscle motor and somatosensory evoked potentials for intramedullary spinal cord tumour surgery. Yonsei Med J . 2014; 55( 4): 1063- 1071. Google Scholar CrossRef Search ADS PubMed  6. Tamkus A, Rice KS, Kim HL. Intraoperative neuromonitoring alarms: relationship of the surgeon's decision to intervene (or not) and clinical outcomes in a subset of spinal surgical patients with a new postoperative neurological deficit. Neurodiag J . 2017; 57( 4): 276- 287. Google Scholar CrossRef Search ADS   7. McCormick Classification. Available at: http://www.surgicalneurology.org/spine/. Copyright © 2018 by the Congress of Neurological Surgeons http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Neurosurgery Oxford University Press

In Reply: Guidelines for the Use of Electrophysiological Monitoring for Surgery of the Human Spinal Column and Spinal Cord

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Publisher
Oxford University Press
Copyright
Copyright © 2018 by the Congress of Neurological Surgeons
ISSN
0148-396X
eISSN
1524-4040
DOI
10.1093/neuros/nyy158
Publisher site
See Article on Publisher Site

Abstract

To the Editor: The authors of the Guidelines for the Use of Electrophysiological Monitoring for Surgery of the Human Spinal Column and Spinal Cord1 are pleased to respond to the letter to the editor regarding this work.2 To begin, it is important to point out that our work was a guideline based upon a systematic review of the literature, and not a meta-analysis. The standards for reporting of guidelines, systematic reviews, and meta-analyses are all quite different and those demanded by the American Association of Neurological Surgeons and the Congress of Neurological Surgeons for guidelines were followed in this publication. We are happy to respond to the points made by the authors of the letter,2 as will be seen below. In 2017, Harel et al3 reported their experience with resection of intradural extramedullary spinal tumors with and without the use of intraoperative electrophysiological monitoring (IOM). Their retrospective, historically controlled study compared 41 patients who underwent tumor resection with the use of IOM with 70 patients who underwent tumor resection without the use of IOM. The authors attempt to evaluate IOM as both a diagnostic tool and a therapeutic adjunct in accordance with a validated medical evidence rating scheme.4 The Bayesian analysis of monitoring alerts and retrospective nature of the study earn a class II medical evidence rating for the use of IOM as a diagnostic tool. Evaluation of postoperative neurological deficit rates in a retrospective, comparative manner (not significant between the 2 groups) earns a class II medical evidence rating for the use of IOM as a therapeutic adjunct. Despite their laudable efforts, the authors admit several study limitations, among them a significantly different rate of instrumentation (0% in the historical control group and 17% in the study group). We agree that this study group discordance is unfortunate, and it does not alter our recommendations. A weak, negative result does not support an argument for therapeutic efficacy. In 2014, Choi et al5 retrospectively evaluated the use of IOM as a therapeutic adjunct in 76 patients who underwent resection of intramedullary spinal cord tumors. Fifty patients who underwent resection with the use of IOM were compared to 26 patients who underwent resection without IOM with respect to rate of gross total tumor resection and neurological outcome. Despite a promising result from the initial, univariate analysis, the authors appropriately conducted a more comprehensive, multivariate analysis to account for numerous patient factors. In their final model, the use of IOM did not result in a statistically significant effect on either rate of gross total tumor resection or neurological outcome. While we agree that sample size and heterogeneity may have influenced the statistical outcomes of this class II medical evidence study, we can only evaluate the study and its results as designed/reported. In the context of a medical evidence-based guidelines document, it is scientifically inappropriate to speculate on how these results might have changed were the study designed differently. The study by Tamkus et al6 was published after submission of the Guidelines for the Use of Electrophysiological Monitoring for Surgery of the Human Spinal Column and Spinal Cord1 and was not included in our published analysis. The authors present an industry-sponsored (Nuvasive Inc, San Diego, California), observational, noncomparative review of patients who underwent spinal column or spinal cord surgery with the use of IOM and were found to have a new or worse postoperative neurological deficit. The relationship of the surgeon's decision to intervene (or not), as well as the nature of that intervention, was compared with respect to rate of improvement in neurological deficit at time of discharge. Industry sponsorship notwithstanding, this study is plagued by numerous statistical and methodological issues and represents class III medical evidence study (at best). The authors provide no baseline demographic statistics for the “intervention” and “no intervention group.” An enormous variety of spinal pathologies encompassing all spinal segments (including lumbosacral) were analyzed in aggregate. No objective measure of baseline or postoperative neurological function (eg, Japanese Orthopaedic Association, McCormick grade, Benzel grade, etc7) was presented. No follow-up data were obtained beyond hospital discharge. All data points were gleaned from IOM technologists’ proprietary records (not from electronic medical records). We agree with the authors that this “study also cannot determine the impact of Intraoperative Neuromonitoring in improving outcomes by preventing postoperative neurologic deficits… [and that] the assumption that there is a causal link between a failure to intervene and a poor outcome may be flawed.” Unfortunately, this study fails to appropriately evaluate IOM as either a diagnostic tool or a therapeutic adjunct. For these reasons, inclusion of this article would not alter our recommendations for the use of IOM in either a diagnostic or therapeutic capacity. Lastly, the difficulty that the authors of the letter2 have in understanding the differences between diagnostic and therapeutic usefulness of IOM shows a lack of understanding of the 2 aspects of tools such as this. IOM is well able to show that an injury has/might have occurred (ie, can make the diagnosis), but it has not been demonstrated that the indications of change in neurological status then lead to surgical (or other) responses that provide for an improved outcome (ie, therapeutic benefit) for spinal surgery patients. In fact, it may not be clear to the team what, if any, maneuver caused the changes, or what, if any, intervention might change the outcome. Their ideas about checklists to improve communication between team members in the operating room are interesting, but well beyond the scope of our guidelines, and do not address the issue of apparent dissociation between diagnosis and therapy. However, we would certainly encourage the authors of the letter to assess whether implementation of such a checklist would produce some evidence that could be used to support (or not) the use of IOM as a therapeutic adjunct in spinal surgery. So far, those data are missing from the literature. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Hadley MN, Shank CD, Rozzelle CJ, Walters BC. Guidelines for the use of electrophysiological monitoring for surgery of the human spinal column and spinal cord. Neurosurgery . 2017; 81( 5): 713- 732. Google Scholar PubMed  2. Wilkinson M, Houlden D. Letter: guidelines for the use of electrophysiologial monitoring for surgery of the human spinal column and spinal cord. Neurosurgery . 2018. doi: 10.1093/neuros/nyy157. 3. Harel R, Schleifer D, Appel S, Attia M, Cohen ZR, Knoller N. Spinal intradural extramedullary tumors: the value of intraoperative neurophysiologic monitoring on surgical outcome. Neurosurg Rev . 2017; 40( 4): 613- 619. Google Scholar CrossRef Search ADS PubMed  4. Walters BC. Methodology of the guidelines for the management of acute cervical spine and spinal cord injuries. Neurosurgery . 2013; 72( suppl 2): 17- 21. Google Scholar CrossRef Search ADS PubMed  5. Choi I, Hyun SJ, Kang JK, Rhim SC. Combined muscle motor and somatosensory evoked potentials for intramedullary spinal cord tumour surgery. Yonsei Med J . 2014; 55( 4): 1063- 1071. Google Scholar CrossRef Search ADS PubMed  6. Tamkus A, Rice KS, Kim HL. Intraoperative neuromonitoring alarms: relationship of the surgeon's decision to intervene (or not) and clinical outcomes in a subset of spinal surgical patients with a new postoperative neurological deficit. Neurodiag J . 2017; 57( 4): 276- 287. Google Scholar CrossRef Search ADS   7. McCormick Classification. Available at: http://www.surgicalneurology.org/spine/. Copyright © 2018 by the Congress of Neurological Surgeons

Journal

NeurosurgeryOxford University Press

Published: Apr 24, 2018

References