Perils of intraoperative neurophysiological monitoring: analysis of "false-negative" results in spine surgeries.

BACKGROUND CONTEXT: Although some authors have published case reports describing false negatives in intraoperative neurophysiological monitoring (IONM), a systematic review of causes of false-negative IONM results is lacking.

PURPOSE: The objective of this study was to analyze false-negative IONM findings in spine surgery.

STUDY DESIGN: This is a retrospective cohort analysis.

PATIENT SAMPLE: A cohort of 109 patients with new postoperative neurologic deficits was analyzed for possible false-negative IONM reporting.

OUTCOME MEASURES: The causes of false-negative IONM reporting were determined.

MATERIALS AND METHODS: From a cohort of 62,038 monitored spine surgeries, 109 consecutive patients with new postoperative neurologic deficits were reviewed for IONM alarms.

RESULTS: Intraoperative neurophysiological monitoring alarms occurred in 87 of 109 surgeries. Nineteen patients with new postoperative neurologic 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. The absence of IONM alarms during these 22 surgeries had different origins: "true" false negatives where no waveform changes meeting the alarm criteria occurred despite the appropriate IONM (7); a postoperative development of a deficit (6); failure to monitor the pathway, which became injured (5); the absence of interpretable IONM baseline data which precluded any alarm (3); and technical IONM application issues (1).

CONCLUSIONS: Overall, 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 a 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 neurologic status. Alarm criteria for IONM may need to be refined for specific procedures and deserves continued study.