Comparing the efficacy of awake and sedated MEG to TMS in mapping hand sensorimotor cortex in a clinical cohort

Abstract

Non-invasive methods such as Transcranial Magnetic Stimulation (TMS) and magnetoencephalography (MEG) aid in the pre-surgical evaluation of patients with epilepsy or brain tumor to identify sensorimotor cortices. MEG requires sedation in children or patients with developmental delay. However, TMS can be applied to awake patients of all ages with any cognitive abilities. In this study, we compared the efficacy of TMS with MEG (in awake and sedated states) in identifying the hand sensorimotor areas in patients with epilepsy or brain tumors. We identified 153 patients who underwent awake- (n = 98) or sedated-MEG (n = 55), along with awake TMS for hand sensorimotor mapping as part of their pre-surgical evaluation. TMS involved stimulating the precentral gyrus and recording electromyography responses, while MEG identified the somatosensory cortex during median nerve stimulation. Awake-MEG had a success rate of 92.35 % and TMS had 99.49 % (p-value = 0.5517). However, in the sedated-MEG cohort, TMS success rate of 95.61 % was significantly higher compared to MEG's 58.77 % (p-value = 0.0001). Factors affecting mapping success were analyzed. Logistic regression across the entire cohort identified patient sedation as the lone significant predictor, contrary to age, lesion, metal, and number of antiseizure medications (ASMs). A subsequent analysis replaced sedation with anesthetic drug dosage, revealing no significant predictors impacting somatosensory mapping success under sedation. This study yields insights into the utility of TMS and MEG in mapping hand sensorimotor cortices and underscores the importance of considering factors that influence eloquent cortex mapping limitations during sedation.

Keywords: Brain tumor; Epilepsy; Magnetoencephalography (MEG); Sedation; Sensorimotor mapping; Transcranial Magnetic Stimulation (TMS).

Fig. 1

Standards for the reporting of diagnostic accuracy studies (STARD) flow chart of participants included in the study. We identified 155 sessions of hand sensorimotor mapping from 153 patients.

Fig. 2

TMS and MEG success rate (at least in one or both hemisphere(s)) in identifying hand sensorimotor cortices in awake- and sedated-MEG groups. The success rates for MEG and TMS were not different in the awake-MEG group while, the MEG success rate was significantly lower when compared to TMS in the sedated-MEG cohort (p = 0.0001, chi-square test).