Direct Cortical Motor Evoked Potential (dcMEP)
An evoked potential that records a response at the peripheral neuromuscular junction from direct stimulation of eloquent cortex.
Monitoring of somatosensory evoked potentials (SEPs) to median and posterior tibial nerve stimulation and monitoring of electromyographic (EMG) activity to direct cortical motor evoked potentials (dcMEPs) were carried out as part of a left frontal lobe craniotomy for tumor resection of unknown etiology. The 45-year-old female patient presents following seizure activity last month. MRIs and CT scans reveal a non-enhancing, infiltrating lesion in the left frontal lobe abutting the supplementary motor area. She has not had any seizure activity after medication and she has no other related neurological deficits. For SEP monitoring, activity was recorded from subdermal needle electrodes placed on the head at Fpz (non-inverting lead) and Cz'/C3’/C4’/Cii (inverting leads). Stimulation rates were 2.79 pulses/second; current levels were 25.0/35.0 mAmps for both left and right wrist/ankle stimulation. For dcMEP monitoring, subdermal needle electrodes were placed in the right orbicularis oris, deltoid, biceps/triceps, thenar/hypothenar, tibialis anterior/gastrocnemius and foot flexor/extensor muscles Stimulation was carried out using a Cadwell Cascade TCS-1 (pulse width-50 microseconds, a train of three pulses, 2.0 ms inter-stimulus interval, constant voltage stimulation ranged from 0-100 volts). Direct cortical stimulation was achieved using a subdermal 6-pin strip electrode placed across the left motor strip. Anodal and cathodal stimulation applied from the most effective pins were used to generate a response from the 6-pin strip electrode. A subdermal paired needle electrode in the right shoulder served as a ground. SEPs/dcMEPs were amplified (gain=105) using differential amplifiers (Cadwell Cascade), averaged and computer monitored (Toshiba). Listed below is a summary of intraoperative activities pertinent to monitoring procedures.
12:15 - Equipment set-up begins.
13:15 - Electrodes placed in the scalp face, wrist/ankles, as well as, upper and lower limb muscle groups bilaterally. No 60 Hz interference noted. Equipment set-up is complete. Anesthesia protocol: propofol - 100 mcg/kg/min, remifentanyl - 0.3 mcg/kg/min. Mean arterial pressure is 70 mm Hg, patient is unparalyzed. Baseline SEPs are as follows: left upper limb - N20 - 19.9 ms, right upper limb - N20 - 19.7 ms, left lower limb - P50 - 47.6 ms, right lower limb - P50 - 47.5 ms. (see fig 1).
Monitoring of somatosensory evoked potentials (SEPs) to median and posterior tibial nerve stimulation and monitoring of electromyographic (EMG) activity to direct cortical motor evoked potentials (dcMEPs) were carried out as part of a left frontal lobe craniotomy for tumor resection of unknown etiology. The 45-year-old female patient presents following seizure activity last month. MRIs and CT scans reveal a non-enhancing, infiltrating lesion in the left frontal lobe abutting the supplementary motor area. She has not had any seizure activity after medication and she has no other related neurological deficits. For SEP monitoring, activity was recorded from subdermal needle electrodes placed on the head at Fpz (non-inverting lead) and Cz'/C3’/C4’/Cii (inverting leads). Stimulation rates were 2.79 pulses/second; current levels were 25.0/35.0 mAmps for both left and right wrist/ankle stimulation. For dcMEP monitoring, subdermal needle electrodes were placed in the right orbicularis oris, deltoid, biceps/triceps, thenar/hypothenar, tibialis anterior/gastrocnemius and foot flexor/extensor muscles Stimulation was carried out using a Cadwell Cascade TCS-1 (pulse width-50 microseconds, a train of three pulses, 2.0 ms inter-stimulus interval, constant voltage stimulation ranged from 0-100 volts). Direct cortical stimulation was achieved using a subdermal 6-pin strip electrode placed across the left motor strip. Anodal and cathodal stimulation applied from the most effective pins were used to generate a response from the 6-pin strip electrode. A subdermal paired needle electrode in the right shoulder served as a ground. SEPs/dcMEPs were amplified (gain=105) using differential amplifiers (Cadwell Cascade), averaged and computer monitored (Toshiba). Listed below is a summary of intraoperative activities pertinent to monitoring procedures.
12:15 - Equipment set-up begins.
13:15 - Electrodes placed in the scalp face, wrist/ankles, as well as, upper and lower limb muscle groups bilaterally. No 60 Hz interference noted. Equipment set-up is complete. Anesthesia protocol: propofol - 100 mcg/kg/min, remifentanyl - 0.3 mcg/kg/min. Mean arterial pressure is 70 mm Hg, patient is unparalyzed. Baseline SEPs are as follows: left upper limb - N20 - 19.9 ms, right upper limb - N20 - 19.7 ms, left lower limb - P50 - 47.6 ms, right lower limb - P50 - 47.5 ms. (see fig 1).