Factors predicting the feasibility of monitoring lower-limb muscle motor evoked potentials in patients undergoing excision of spinal cord tumors

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>This prospective study on intraoperative muscle motor evoked potentials (MMEPs) from lower-limb muscles in patients undergoing surgery for spinal cord tumors was performed to: 1) determine preoperative clinical features that could predict successful recording of lower-limb MMEPs; 2) determine the muscle in the lower limb from which MMEPs could be most consistently obtained; 3) assess the need to monitor more than 1 muscle per limb; and 4) determine the effect of a successful baseline MMEP recording on early postoperative motor outcome.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>Of 115 consecutive patients undergoing surgery for spinal cord tumors, 110 were included in this study (44 intramedullary and 66 intradural extramedullary tumors). Muscle MEPs were generated using transcranial electrical stimulation under controlled anesthesia and were recorded from the tibialis anterior, quadriceps, soleus, and external anal sphincter muscles bilaterally. The effect of age (≤ 20 or &gt; 20 years old), location of the tumor (intramedullary or extramedullary), segmental location of the tumor (cervical, thoracic, or lumbar), duration of symptoms (≤ 12 or &gt; 12 months), preoperative functional grade (Nurick Grades 0–3 or 4–5), and muscle power (Medical Research Council Grades 0/5–3/5 or 4/5–5/5) on the success rate of obtaining MMEPs was studied using multiple regression analysis. The effect of the ability to monitor MMEPs on motor outcome at discharge from the hospital was also analyzed.</jats:p></jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>The overall success rate for obtaining baseline lower-limb MMEPs was 68.2% (75 of 110 patients). Eighty-nine percent of patients with Nurick Grades 0–3 had successful MMEP recordings. Muscle MEPs could not be obtained in any patient in whom muscle power was 2/5 or less, but were obtained from 91.4% of patients with muscle power of 4/5 or more. Analysis showed that only preoperative Nurick grade (p ≤ 0.0001) and muscle power (p &lt; 0.0001) were significant predictors of the likelihood of obtaining MMEPs. Responses were most consistently obtained from the tibialis anterior muscle (68%), but in the other 32% MMEPs could not be recorded from the tibialis anterior but could be recorded from another muscle. The ability to monitor MMEPs was associated with better motor outcome at discharge from the hospital (p = 0.052).</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>The likelihood of obtaining lower-limb MMEPs is significantly greater in patients with better functional grades and higher motor power. Muscle MEPs are most consistently obtained from the tibialis anterior muscle but other muscles should also be monitored to optimize the chances of obtaining MMEP responses from the lower limbs.</jats:p></jats:sec>

Multi-channel motor evoked potential monitoring during anterior cervical discectomy and fusion

“…Secondly, we did not analyze the preoperative motor weakness of patients with unobtainable baseline MEPs. Indeed, a previous study indicated that successful MEP recordings were possible in only 27.5% patients with an MRC grade 0–3 (Rajshekhar et al, 2011). …”

Intraoperative neurophysiological mapping and monitoring in spinal tumor surgery: sirens or indispensable tools?

“…Muscle MEPs (mMEPs) are a reliable technique for monitoring motor pathways. 41,44 Transcranial electrical stimulation with a multipulse technique is used for eliciting mMEPs and includes short trains of 5 square-wave stimuli (single pulse duration 0.5 msec, interstimulus in-terval 4 msec, rate 2 Hz) through corkscrew electrodes placed at C1/C2 (lower limbs) and C3/C4 (upper limbs) scalp sites. The mMEPs are recorded through needle electrodes inserted into the upper-and lower-extremity muscles; they do not require averaging, but they do have wide amplitude and morphological variability.…”

Surgical Management of Spinal Intramedullary Tumors: Radical and Safe Strategy for Benign Tumors

“…Rajshekhar et al showed that 89% of patients with preoperative Nurick grades of 0–3 provided successful recordings, compared to only 7.1% of patients with preoperative Nurick grades of 4–5. 26) …”