====== Direct cortical motor evoked potentials ======

[[Transcranial motor evoked potentials]] and direct [[cortical motor evoked potentials]] (DCMEP) paradigms have historically been used contemporaneously or independently during [[supratentorial]] [[craniotomy]]. The use of DCMEPs for [[monitoring]] the [[corticospinal tract]]s during [[craniotomy]] has been well described 
((Taniguchi M, Cedzich C, Schramm J. Modification of [[cortical stimulation]] for [[motor evoked potentials]] under general anesthesia: technical description. Neurosurgery. 1993 Feb;32(2):219-26. doi: 10.1227/00006123-199302000-00011. PMID: 8437660.))
((Somatosensory evoked potential phase reversal and direct motor cortex stimulation during surgery in and around the central region. Cedzich C, Taniguchi M, Schäfer S, Schramm J. https://www.ncbi.nlm.nih.gov/pubmed/8727822. Neurosurgery. 1996;38:962–970.))
((Identification of motor pathways during tumor surgery facilitated by multichannel electromyographic recording. Yingling CD, Ojemann S, Dodson B, Harrington MJ, Berger MS. https://www.ncbi.nlm.nih.gov/pubmed/10584836. J Neurosurg. 1999;91:922–927.))
((Intra-operative mapping of the motor cortex during surgery in and around the motor cortex. Kombos T, Suess O, Funk T, Kern BC, Brock M. https://www.ncbi.nlm.nih.gov/pubmed/10819256. Acta Neurochir (Wien) 2000;142:263–268.))
((Intraoperative mapping and monitoring of the corticospinal tracts with neurophysiological assessment and 3-dimensional ultrasonography-based navigation. Clinical article. Nossek E, Shahar K, Kanner A, et al. https://www.ncbi.nlm.nih.gov/pubmed/20799862. J Neurosurg. 2011;114:738–746.)).

DCMEP has many advantages over TCMEP monitoring. For example, there is limited-to-no patient movement; therefore, the stimulation can be conducted continuously throughout a procedure allowing for real-time feedback of [[motor system]] integrity. DCMEP also allows for a more focal superficial [[stimulation]]. Using a single contact from a [[strip]] or [[grid]] electrode placed directly on the exposed [[cortex]] allows for the use of comparatively lower stimulation intensity, therefore, reducing current density, current spread, and deep penetration of stimuli
((Intraoperative [[mapping]] and monitoring of [[motor cortex]] - a new paradigm. Yingling C. US Neurol. 2011;7:64–67.))

===== Case reports =====
A 12-year-old girl required [[general anesthesia]] under intraoperative direct cortical [[motor evoked potentials]] monitoring due to supratentorial [[glioma]]. [[Remimazolam]]-based anesthesia was selected, instead of [[propofol]], due to the patient's egg hypersensitivity. Stable myogenic MEPs were recorded throughout the surgery with remimazolam at 0.9 mg/kg/h and remifentanil at 0.35 μg/kg/min, following adjustments of stimulation intensity and titration of remimazolam infusion. Neither intraoperative memory nor motor deficits were present after surgery.

Kamata et al. presented a pediatric case whose dc-MEP was recorded under remimazolam anesthesia. The cardiovascular stability and avoidance of propofol infusion syndrome with remimazolam were superior to propofol
((Kamata K, Asagi S, Shimoda Y, Kanamori M, Abe N, Sugino S, Tominaga T, Yamauchi M. Successful recording of direct cortical motor-evoked potential from a pediatric patient under remimazolam anesthesia: a case report. JA Clin Rep. 2022 Aug 22;8(1):66. doi: 10.1186/s40981-022-00555-y. PMID: 35989409.)).
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A 65-year-old female underwent a supratentorial craniotomy for the clipping of a right-sided unruptured middle cerebral artery (MCA) aneurysm. DCMEP recordings of the upper extremity degraded after the parent vessel was temporarily occluded with a clip. The recordings returned once the clip was released. The DCMEP lower extremity recordings did not deviate from their established baseline. TCMEP recordings (upper and lower extremities) also did not differ from their established baselines. The permanent clip was placed without incident, and the patient awoke neurologically intact. This case study demonstrates the specificity and sensitivity of DCMEP vs. TCMEP. DCMEP activates the corticospinal tract more superficially; therefore, it was evident by the loss of the upper extremity DCMEPs without the loss of lower extremity DCMEPs that the temporary vessel occlusion caused an ischemic event focal to the cortical area perfused by the MCA. TCMEP did not detect this ischemic event
((Silverstein JW, Rosenthal A, Ellis JA. Direct Cortical Motor Evoked Potentials Versus Transcranial Motor Evoked Potentials for the Detection of Cortical Ischemia During Supratentorial Craniotomy: Case Report. Cureus. 2018 Dec 24;10(12):e3771. doi: 10.7759/cureus.3771. PMID: 30820390; PMCID: PMC6389021.)).