Adam T. Doan, DC, DABNM, Vice President, Clinical Services and Richard Vogel, PhD, D.ABNM, FASNM, Director, Clinical Services at SafePassage have completed a comprehensive summary and analysis of the following article:
“Perils of intraoperative neurophysiological monitoring: analysis of “false-negative” results in spine surgeries” published in The Spine Journal, February 20181.
Although the use of intraoperative neuromonitoring (IONM) has been demonstrated to yield a high sensitivity, specificity, and negative predictive value, there are still numerous occasions where false data is possible. The use of a multimodal IONM strategy has decreased the rate of false negative reporting, as complimentary tests are available to assess both the sensory and motoric neural tissue at risk during spine surgery. This recently published study analyzed the rate of one practice’s false negative data and lends valuable information regarding how to approach and improve this rare event.
Of the 62,038 surgeries included in this retrospective study, there were 22 documented false negative events (0.04% of cases). Although no diagnostic test or interventional strategy is perfect, and there are known limitations to all neuromonitoring modalities, it’s worth exploring the included table where the authors delve deeper into each of these 22 outcomes. In six of these cases, the patient emerged from anesthesia intact, but developed a delayed deficit. IONM is only designed to detect conduction changes corresponding to the time of testing and will not pick up an injury occurring in the postoperative period. Omitting these “false negatives” from the study would improve the negative predictive value and would decrease the occurrence rate to approximately 0.03% of cases.
Three of the remaining 17 patients had absent baseline data, which ultimately proved to be indicative of a new postoperative deficit. These findings may be secondary to baseline recordings being collected after risk-prone maneuvers had occurred (e.g. patient positioning). The purest IONM data collection begins prior to known times of risk when the patient is in their most neutral state. Five of these patients had deficits in unmonitored pathways. It behooves the neuromonitoring team to have an ongoing dialogue with the OR stakeholders regarding the pros, cons and limitations of all monitoring choices, and this collective group needs to always be on the same page regarding protocols. If motor data is not collected during a procedure, it cannot be expected that our sensory modalities will be reflective of intraoperative or postoperative motor status. The same holds true for all IONM tests, and the risk versus benefit of the plan should be discussed in collaboration with the surgeon and anesthesia team.
The remaining 8 patients display the complexity and imperfectness of the science and are in some ways a roadmap of the work to be done in the profession: spontaneous EMG as a unimodal strategy to indicate motor function has limitations; pedicle screw stimulation is prone to technical flaws in methodology; IONM tests do not measure pain, and are therefore insensitive to new radiculopathy in the absence of sensorimotor deficit; there is no one-size-fits-all alert criterion for motor evoked potentials, etc. Not unlike surgery, IONM is an art form in addition to an ever-evolving science.
The take-home message is that the IONM false-negative patient is very rare when using a multimodal strategy in experienced hands with a collaborative approach where communication and teamwork is sound. Despite the rarity of the event, there will still be times when a new deficit occurs with no warning. Often, this likelihood can be mitigated and ultimately improved with an ongoing dialogue about the value and utility of each test that is chosen (or not) to monitor a particular patient, with sound teamwork to foster the best IONM for each individual patient encounter.
1Tamkus AA, Rice KS, McCaffrey MT. Perils of intraoperative neurophysiological monitoring: analysis of “false-negative” results in spine surgeries. Spine J 2018; 18(2):276-84.