Perils of intraoperative neurophysiologic monitoring: analysis of ‘false negative’ results in spine surgeries

Publication date: Available online 13 July 2017
Source:The Spine Journal
Author(s): Arvydas Tamkus, Kent S. Rice, Michael McCaffrey
Background contextAlthough some authors published case reports describing false negatives in intraoperative neurophysiologic monitoring (IONM), systematic review of causes of false negative IONM results is lacking.PurposeThe objective was to analyze false negative IONM findings in spine surgery.Study designRetrospective cohort analysisPatient sampleA cohort of 109 patients with new postoperative neurological deficits was analyzed for possible false negative IONM reporting.Outcome measuresCauses of false negative IONM reporting were determined.MethodsFrom a cohort of 62,038 monitored spine surgeries, 109 consecutive patients with new postoperative neurological deficits were reviewed for IONM alarms.ResultsIONM alarms occurred in 87/109 surgeries. Nineteen patients with new postoperative neurological deficits did not have an IONM alarm and surgeons were not warned. In addition, three patients had no interpretable IONM baseline data and no alarms were possible for the duration of the surgery. Therefore 22 patients were included in the study. Absence of IONM alarms during these 22 surgeries had different origins: "True" false negatives where no waveform changes meeting alarm criteria occurred despite appropriate IONM (7); postoperative development of a deficit (6); failure to monitor the pathway which became injured (5); absence of interpretable IONM baseline data which precluded any alarm (3); and technical IONM application issues (1).ConclusionsOverall the rate of IONM method failing to predict the patient's outcome was very low (0.04% - 22/62,038). Minimizing false negatives requires the application of proper IONM technique with the limitations of each modality considered in their selection and interpretation. Multimodality IONM provides the most inclusive information and although it might be impractical to monitor every neural structure that can be at risk, a thorough preoperative consideration of available IONM modalities is important. Delayed development of postoperative deficits cannot be predicted by IONM. Absent baseline IONM data should be treated as an alarm when inconsistent with the patient's preoperative neurological status. Alarm criteria for IONM may need to be refined for specific procedures and deserves continued study.



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