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Motor evoked potentials

Motor evoked potential (MEP) is used to monitor motor function, and is the most important in neurosurgical operations 1) 2).

There is evidence that monitoring of motor evoked potentials (MEPs) is useful in preventing and predicting postoperative motor deficit during surgery for supratentorial lesions 3) 4).

Transcranial electrical MEPs could be implemented during neurosurgery in infants between 1 and 3 months of age. Intraoperative MEP monitoring may be a safe adjunct for neurosurgical procedures in these very young patients 5).

Two stimulation modalities have been established to elicit MEPs—transcranial electrical stimulation (TES) and direct cortical stimulation.

MEP has become popular due to the recent rapid advances with propofol anesthesia and the train stimulation method 6) 7).

In adult neurosurgical patients with a normal motor status, a train of 5 pulses and an interstimulus interval (ISI) of 3 ms provide the lowest motor thresholds. Joksimovic et al. provided evidence of the dependence of required stimulation current on ISI 8).

Continuous motor mapping using subcortical stimulation via a surgical aspirator, in comparison with the sequential use of a standard monopolar stimulation probe, is a feasible and safe method without any disadvantages. Compared with the standard probe, the aspirator offers continuous information on the distance to the corticospinal tract 9).

Vasospasm following aneurysmal subarachnoid hemorrhage (aSAH) can be detected accurately by using MEPs. MEPs are a feasible bedside tool for online VS detection in an intensive care unit and, therefore, may complement existing diagnostic tools 10)

see Transcranial motor evoked potential monitoring.

Redondo-Castro et al have applied transcranial electrical stimulation to rats with spinal cord injury and selectively tested the motor evoked potentials (MEPs) conveyed by descending motor pathways with cortical and subcortical origin. MEPs were elicited by electrical stimulation to the brain and recorded on the tibialis anterior muscles. Stimulation parameters were characterized and changes in MEP responses tested in uninjured rats, in rats with mild or moderate contusion, and in animals with complete transection of the spinal cord. All injuries were located at the T8 vertebral level. Two peaks, termed N1 and N2, were obtained when changing from single pulse stimulation to trains of 9 pulses at 9 Hz. Selective injuries to the brain or spinal cord funiculi evidenced the subcortical origin of N1 and the cortical origin of N2. Animals with mild contusion showed small behavioral deficits and abolished N1 but maintained small amplitude N2 MEPs. Substantial motor deficits developed in rats with moderate contusion, and these rats had completely eliminated N1 and N2 MEPs. Animals with complete cord transection had abolished N1 and N2 and showed severe impairment of locomotion. The results indicate the reliability of MEP testing to longitudinally evaluate over time the degree of impairment of cortical and subcortical spinal pathways after spinal cord injuries of different severity 11).

Case series

Yi et al., from the Seoul National University Hospital investigated 25 cases in which infants younger than 3 months (mean age 72.8 days, range 39-87) underwent neurosurgery between 2014 and 2017. Myogenic MEPs were obtained through transcranial electrical stimulation. In all cases, surgery was performed under total intravenous anesthesia, maintained with remifentanil and propofol.

MEPs were documented in 24 infants, the sole exception being 1 infant who was lethargic and had 4-limb weakness before surgery. The mean stimulation intensity maintained during monitoring was 596 ± 154 V (range 290-900 V). In 19 of 24 infants MEP signals remained at ≥ 50% of the baseline amplitude throughout the operation. Among 5 cases with a decrease in intraoperative MEP amplitude, the MEP signal was recovered in one during surgery, and in the other case a neurological examination could not be performed after surgery. In the other 3 cases, 2 infants had relevant postoperative weakness and the other did not show postoperative neurological deficits. Postoperative weakness was not observed in any of the 20 infants who had no deterioration (n = 19) or only temporary deterioration (n = 1) in MEP signal during surgery.

Transcranial electrical MEPs could be implemented during neurosurgery in infants between 1 and 3 months of age. Intraoperative MEP monitoring may be a safe adjunct for neurosurgical procedures in these very young patients 12).


Burke D, Hicks RG. Surgical monitoring of motor pathways. J Clin Neurophysiol. 1998;15:194–205.
Kombos T, Kopetsch O, Suess O, Brock M. Does preoperative paresis influence intraoperative monitoring of the motor cortex? J Clin Neurophysiol. 2003;20:129–34.
Kombos T, Picht T, Derdilopoulos A, Suess O: Impact of intraoperative neurophysiological monitoring on surgery of high-grade gliomas. J Clin Neurophysiol 26:422–425, 2009
Talacchi A, Turazzi S, Locatelli F, Sala F, Beltramello A, Alessandrini F, et al: Surgical treatment of high-grade gliomas in motor areas. The impact of different supportive technologies: a 171-patient series. J Neurooncol 100:417–426, 2010
5) , 12)
Yi YG, Kim K, Shin HI, Bang MS, Kim HS, Choi J, Wang KC, Kim SK, Lee JY, Phi JH, Seo HG. Feasibility of intraoperative monitoring of motor evoked potentials obtained through transcranial electrical stimulation in infants younger than 3 months. J Neurosurg Pediatr. 2019 Mar 15:1-9. doi: 10.3171/2019.1.PEDS18674. [Epub ahead of print] PubMed PMID: 30875681.
Biebuyck JF. Propofol. An update on its clinical use. Anesthesiology. 1994;81:1005–43.
Neuloh G, Pechstein U, Schramm J. Motor tract monitoring during insular glioma surgery. J Neurosurg. 2007;106:582–92.
Joksimovic B, Damjanovic A, Damjanovic A, Rasulic L. Transcranial Electric Stimulation for Intraoperative Motor Evoked Potential Monitoring: Dependence of Required Stimulation Current on Interstimulus Interval Value. J Neurol Surg A Cent Eur Neurosurg. 2015 Jan 16. [Epub ahead of print] PubMed PMID: 25594816.
Shiban E, Krieg SM, Obermueller T, Wostrack M, Meyer B, Ringel F. Continuous subcortical motor evoked potential stimulation using the tip of an ultrasonic aspirator for the resection of motor eloquent lesions. J Neurosurg. 2015 May 15:1-6. [Epub ahead of print] PubMed PMID: 25978712.
Grossauer S, Koeck K, Kraschl J, Olipitz O, Hausegger KA, Vince GH. Detection of Cerebral Vasospasm Following Aneurysmal Subarachnoid Hemorrhage Using Motor Evoked Potentials. Neurosurgery. 2016 Feb;78(2):265-73. doi: 10.1227/NEU.0000000000001040. PubMed PMID: 26421589.
Redondo-Castro E, Navarro X, García-Alías G. Longitudinal Evaluation of Residual Cortical and Subcortical Motor Evoked Potentials in Spinal Cord Injured Rats. J Neurotrauma. 2016 May 15;33(10):907-16. doi: 10.1089/neu.2015.4140. Epub 2016 Jan 28. PubMed PMID: 26560177.
motor_evoked_potentials.txt · Last modified: 2019/03/16 19:31 by administrador