In this blog post, one of our members stepped up to the challenge of helping us review recent papers from the literature. Many thanks to Christopher Halford! If any readers would like help by writing summaries of recent papers, please contact me (ASNM President Rich Vogel). The post below was written by Christopher D. Halford BA, R. EEG/EP T., CNIM.
In the article "Postoperative navigated transcranial magnetic stimulation to predict motor recovery after surgery of tumors in motor eloquent areas" by Seidel, et al., published in the June 2019 edition of Clinical Neurophysiology, the authors approach a very interesting topic. As the title says, they attempted to use post-operative transcranial magnetic stimulation (TMS) on patients to see if a present MEP could predict patient recovery following an intraoperative change in dcMEPs and/or tcMEPs that resulted in a post-operative motor deficit.
Throughout the article the authors explain their methodology in great detail. They included essential information like the majority of the standards they used for establishing their criteria for changes in intraoperative MEP testing, the time frame used in the study to test the patient post-op, and a detailed chart showing the important information for each patient in the study including pre- and post-op strength changes, individual intraoperative MEP change (with recovery of signal or a lack thereof), recovery of strength from day one, one week, and one month post-op, etc. The authors make educating the reader of their testing and results, along with prior research done in this area (with many citations of pertinent scholarly articles to support each statement of fact or claim that guided their methods) a very high priority of their publication.
All of the 13 patients included in this study presented with a decrease in post-operative motor function compared to their pre-op exam. Within one week post-op (average=3.8 days) the researchers tested each patient and were able to record an MEP through navigated transcranial magnetic stimulation in 11 of the 13 patients. Ten of the 11 that had had a recordable MEP after TMS demonstrated a positive functional recovery by 30 days post-op, demonstrating this method has a positive predictive value (PPV) of 90.9%. Of the remaining two that did not have a post-op MEP after navigated TMS both had minimal to no recovery of function after one month post-op while one patient that had a post-op MEP from magnetic stimulation did not show improvement (based off of their progress criteria).
In this article Seidel et al. show the reader the basis for his study done by other researchers (whose evidence and findings are stated and cited in this article) but they also expand these conclusions as well. As they point out, they extend their testing and results to lower limb motor function (as well as including upper limb) and propose the value of this technique for possible determination of patients that might benefit from aggressive post-op therapy that may have otherwise been seen as candidates that would benefit little from it. Also, the authors offer the prospective benefit of TMS for assessing more secondary and/or associative motor areas of the brain in a way not possible using only intraoperative tc or dcMEPs, which was also one of the key focuses of their testing.
The authors are very good about citing the sample size as the biggest limitation of their study. However with the solid outcomes of this limited sample size the authors have demonstrated that additional research will likely have merit. They also acknowledge that though the tumor locations for each resection were in different eloquent areas, each did have a limit of 3 to 8-cms distance from motor eloquent areas. Although the authors did inform the reader of most of their intraoperative criteria for evaluating and reporting change, it is still somewhat incomplete given that they didn’t list what specific surgical maneuvers were/could have been used to respond to intraoperative MEP changes, once an alarm criteria had been met. Also, more detailed stim parameters, anesthesia regimen/changes, and individual alarm criteria for each intraoperative change would be valuable for study reproduction. As mentioned they did provide much of these aspects but these key components would be crucial for complete replication.
The IONM Big Picture Perspective:
The article offers a potential technique of great value: a method that might indeed help determine the likelihood that a post-operative deficit is either going to be transient or permanent. Although this is an incredibly valuable determination (both to surgeons and patients/families), adaptation of this into the clinical setting could be a difficult task considering the cost of magnetic stimulators to those hospitals and facilities that don’t have preexisting needs for this technology. However, for those that do have this technology onsite, this could be a tremendous opportunity to consider research opportunities. If larger, repeated studies could further support the preliminarily data shown in this current article, then it could serve as evidential support for convincing hospitals to invest the necessary funds to acquire this technology and implement this type of monitoring. The development of a neuromonitoring test that would allow a surgeon to tell a patient, with confidence, that their new deficit will be only temporary has the potential to be a critical area where neuromonitoring could directly contribute to improving patient care. I encourage those that have the interest and the means to help to contact the authors, compile all information needed to replicate the study and move this research forward.
Seidel, K., Hani, L., Lutz, K., Zbinden, C., Redmann, A., Consuegra, A., . . . Schucht, P. (2019). Postoperative navigated transcranial magnetic stimulation to predict motor recovery after surgery of tumors in motor eloquent areas. Clinical Neurophysiology,130(6), 952-959.
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