Utility of Decremental Triggered Electromyogram for Intraoperative Neuromonitoring to Identify Midline in Posterior Myelotomy for Spinal Cord Intramedullary Lesions: Technical Note of a Novel Method.

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Intramedullary spinal cord lesions are eloquent lesions that are surgically resected via posterior midline myelotomy (PMM). This treatment method carries the risk of postoperative neurological deficits. Various intraoperative neuromonitoring techniques have been used to address this concern. Our study aimed to highlight a newly developed monitoring technique (decremental-triggered electromyogram [dtEMG]) as a novel method to identify the spinal cord midline during PMM. Seven patients in prone position underwent PMM for an intramedullary lesion using dtEMG for neuromonitoring. dtEMG was used to determine the threshold amplitude (ie, the lowest amplitude to elicit an EMG response) as well as a silent zone, which was determined to be the midline. The age range was 26-73 years. dtEMG detected a silent zone in 6/7 patients. The only patient in whom dtEMG was not useful was a patient with complete paraplegia and sensory loss before surgery. There were no motor evoked or somatosensory evoked potential changes related to PMM in these patients. Although the commonly used neuromonitoring techniques, including motor and sensory evoked potentials and free-run electromyograms are of utmost importance in spinal cord surgery, they lack the potential to identify midline in such cases. The currently available tools, including dorsal column mapping, are more cumbersome to use. The newly proposed dtEMG technique can safely and efficiently identify the midline when used as an intraoperative neuromonitoring technique in PMM for spinal cord intramedullary lesion resection.