Intraoperative Neuromonitoring (IONM) Is There a Role in Metastatic Spine Tumor Surgery?
The Big Question:
Can Intraoperative Neuromonitoring (IONM) make an impact on surgeons’ efforts to preserve patient quality of life during Metastatic Spinal Tumor Surgery (MSTS)? The team of Kumar et al. published a retrospective study over the past year taking a closer look at the correlation between neuromonitoring utilization and the impact on the surgical outcome. Did the data they uncovered suggest that IONM utilization during MSTS procedures makes an impact on patient outcomes?
Cancer is a nasty business, often causing loss of motor and sensory function in the course of its progression. Our business in neuromonitoring is to provide the surgical team with the information they need to optimally preserve motor and sensory function within the constraints of the surgical procedure. When surgery becomes part of the treatment plan for a patient with spinal metastases, surgeons often need to weigh risk versus reward. Can a sufficient level of pain relief and preservation of function be achieved in light of possible further post-surgical deficits? IONM becomes useful to a surgeon in these cases, and we as the neuromonitoring community stand to make a crucial difference in the patient’s quality of life.
The team of Kumar, et al. – consisting of specialists in ortho, trauma and spinal surgery – astutely noted a lack of literature quantifying the relationship between IONM and MSTS patient outcomes. They engineered a retrospective study of 135 patients over the course of a seven -year time frame to match relationships between significant event alerts and patient outcome for MSTS patients.
The study spans a seven-year period and includes surgical procedures on 135 patients, all with spinal cord metastases from various sources (the article provides a breakdown in table format, with lung and breast carcinomas being primary instigators). The 135 surgical procedures were all performed by one of five surgeons and were monitored by one of two certified neuromonitoring technologists.
Monitoring was performed under and anesthetic regimen suited for TcMEP, EMG and somatosensory modalities. Total Intravenous Anesthesia (TIVA) using fentanyl and propofol were administered to maintain an anesthetized state throughout the procedure. Short-acting paralytics were administered during the intubation phase only, and Train of Four (TOF) was monitored during the surgical procedure to confirm absence of paralytic effect on the patient.
From a neuromonitoring perspective, patients were monitored on two different platforms the Nuvasive NVM5 and the Cadwell Elite system, employing from 20-32 channels depending on monitoring package and surgical approach. All MEP data was elicited from transcranial stimulation from electrode sites C1 and C2. Recording muscle groups ranged from deltoid, biceps brachii, brachioradialis, abductor digiti minimi, vastus medialis, tibialis anterior, extensor hallucis longus, abductor hallucis longus, and gastrocnemius, while somatosensory data was elicited from stimulation of the ulnar, median, and posterior tibial (PTN) nerves. Somatosensory alert criteria included the ’50-10’ rule, or greater than 50 percent loss from baseline amplitude and greater than 10 percent increase in latency from baseline. TcMEP responses were reported as either present or absent, and EMG alerts were reported upon observing “irregular, aperiodic bursts repeatedly elicited by surgical maneuvers greater than a 3 second period” (Kumar, et al. 2019).
A note about the patient population. Of the 135 patients included in the study, seven were eliminated from data inclusion in the retrospective due to a lack of baseline data (i.e., no followable baselines to report to the surgeon, either sensory or motor). This narrows the field to 128 patients whose monitoring experiences contributed to the final report. The population consisted of 61 males and 67 females who were on average 61 years of age.
Patients were scored pre-operatively based on the impact the metastases had on their quality of life using the ASIA score, so a note here about this format may be useful. ASIA stands for American Spinal Injury Association, and the ASIA pre-operative score assesses motor and sensory function of a patient with a spinal injury. The exact nature of the testing and scoring is perhaps a bit too complex for the scope of this literature review, but it is worth knowing some basics. Ten muscle groups are assessed for motor function, five upper extremity and five lower extremity muscles, using range of motion (ROM), ability to move a limb against the force of gravity, active resistance, etc. Sensation is assessed with pin prick applications along a series of dermatomes. A final letter grade is assigned to a patient; A, B, C, D or E. Patients with a grade of E will have what is considered normal sensory and motor function, while letter grades B, C, and D cover patients with incomplete spinal cord injuries, demonstrating some deficits in motor or sensory function. A patient with a grade of A has what is deemed a ‘complete’ injury and exhibits no motor or sensory function for purposes of ASIA scoring (SCIRE Project, 2016).
From a surgical perspective, of the 128 patients, 54 patients had surgery to address a neurological deficit, 66 underwent a procedure for instability pain and 8 were listed as going under the knife for intractable pain. As mentioned earlier, seven patients were excluded from the study due to their ASIA scores; 5 patients had an ASIA score of A (total injury) and 2 had an ASIA score of C – all seven patients failed to present baseline data sufficient for monitoring and reporting to the surgeon during the procedure.
Of 128 with spinal cord metastases who underwent surgical procedures with neuromonitoring, 13 patients had significant alerts. That amounts to 10.2% of the patient population, or 1 in 10 patients. Five patients had TcMEP alerts, 5 patients had TcMEP and somatosensory alerts, 2 patients experienced MEP and EMG alerts, while one patient had alerts in all three modalities.
Of the 128 patients included in the study, there were 114 true negatives, 13 true positives, and 1 false negative. No false positive was reported. Of the 114 procedures resulted in true negatives – no significant alerts were reported during the procedure and the patient woke up without additional deficits. Of the 13 patients with true positives – patients where an alert was reported and either corrections resulted in a return to baseline, or the patient awoke with a deficit - occurred in 9 open procedures and 4 minimally invasive Surgical (MIS) procedures.
The paper further breaks down the true positives into three groups – Group A, Group B and Group C. Group A included one patient (8.3% of the true positive patient population) who exhibited a decrease of signals during a lateral psoas approach. The patient’s responses returned to baseline after the surgeon changed the plane through which the muscle dissection approach occurred. Group B incorporated 5 patients (38.46% of the patient total) who experienced alerts during instrumentation. Four of these patients’ data returned to baseline after either pedicle screw placement adjustment or decreasing the size of the interbody cage placed. One of the patients in Group B did not experience data recovery to baseline after all available interventions were exhausted, and this patient did wake up with complete paraplegia.
Finally, Group C included 7 patients (53.84% of true positives reported) where a significant alert was communicated during the decompression phase of the operating, and these patients all returned to baseline after the decompression was complete.
The final patient was reported as a false negative; the patient awoke with a C5 palsy post-operative after undergoing a cervical laminectomy with hardware placement. Specifically, the right deltoid and biceps function degraded from a grade 5 to 2 immediately upon wakeup assessment. The patient did recover to normal status at the 9-month post-operative mark. This completes the total of procedures with a post-operative deficit; one true positive and one true negative, or 1.6% of the patient population.
The authors conclude that IONM exhibited a high degree of sensitivity and specificity for detecting changes to neurologic status intraoperatively during MSTS procedures. Of particular note is that a number of patients experienced changes in Somatosensory and motor data during the procedure that resolved after intervention by the surgical team. These interventions included changing the surgical approach, trying a different placement or size of hardware, elevating patient’s mean arterial pressure or administering steroids depending on the scenario.
Many of these patients’ IONM data changes resolved at that time, lending support to the concept that effective use of IONM can allow a surgeon to make informed course corrections during a procedure, mitigating the potential for post-operative deficits. The goal in MSTS procedures is often to improve quality of life, either by reducing pain or restoring sensation and function when possible. Surgical actions and conditions that put the patient at risk of incurring further post-operative deficits can be countermanded with use of IONM, making neuromonitoring a powerful tool in the surgeon’s kit when the procedural goal is to improve the patient’s quality of life. The highest degree of accuracy reported in the study was with multimodal IONM, including TcMEP, somatosensory and EMG recording, both passively and with triggered mapping of nervous structures. This was followed by SSEPs in combination with TcMEP, EMG with SSEPs, and finally the lowest diagnostic sensitivity was produced when each of these modalities were used individual during a procedure, and not in concert with other IONM approaches. This finding reinforces the principle that neuromonitoring is at its best when we as professionals can use the full range of our monitoring tools to produce the best results.
The article dives down in the one instance of a false negative included in the study, concluding it was likely a technical error, but providing no further description. This paper provides an encouraging report on the impact of IONM on patient quality of life post-operatively when facing the challenges of spinal cord tumor metastases. While the retrospective study is limited by the constraints of providing data from only two monitoring professionals in the service of five surgeons at one facility, the authors begin to fill in a literature gap that is much needed. More information from other facilities reported in this manner on the impact of IONM on MSTS procedures will be of great benefit to the neuromonitoring community.
- Kumar N, G V, Ravikumar N, Ding Y, Yin ML, Patel RS, Naresh N, Hey HWD, Lau LL, Liu G. Intraoperative Neuromonitoring (IONM): Is There a Role in Metastatic Spine Tumor Surgery? Spine (Phila Pa 1976). 2019 Feb 15;44(4):E219-E224.
- Noona, V., Mak, J., Zhu, J., Diab, K., Queree, M. (2016). American Spinal Injury Association Impairment Scale (AIS): International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI). Retrieved from https://scireproject.com/ (2020).
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