Abstracts

Mapping Primary Motor Cortex in Very Young Children Using Transcranial Magnetic Stimulation

Abstract number : 1.176
Submission category : 3. Neurophysiology / 3E. Brain Stimulation
Year : 2022
Submission ID : 2205037
Source : www.aesnet.org
Presentation date : 12/3/2022 12:00:00 PM
Published date : Nov 22, 2022, 05:27 AM

Authors :
Roozbeh Rezaie, PhD – Le Bonheur Children's Hospital Neuroscience Institute and University of Tennessee Health Science Center at Memphis; Basanagoud Mudigoudar, MD – Associate Professor, Department of Pediatrics, Division of Pediatric Neurology, University of Tennessee Health Science Center; Negar Noorizadeh, Ph.D. – Neuroscience Institute – Le Bonheur Children's Hospital, Memphis, TN; Theresa Williard, BS, RN – MEG/TMS program manager, Neuroscience Institute, Le Bonheur Children's Hospital, Memphis, TN; Neuroscience Institute, Le Bonheur Children's Hospital, Memphis, TN; James Wheless, MD – Professor and Division Chair, Department of Pediatrics, Division of Pediatric Neurology, University of Tennessee Health Science Center, Memphis, TN; Neuroscience Institute, Le Bonheur Children's Hospital, Memphis, TN; Shalini Narayana, Ph.D. – Professor, Department of Pediatrics, Division of Pediatric Neurology, University of Tennessee Health Science Center, Memphis, TN; Neuroscience Institute, Le Bonheur Children's Hospital, Memphis, TN

Rationale: Precise mapping of motor cortex is critical in the presurgical evaluation of intractable focal epilepsy and patients undergoing surgery for brain tumor. Assessing motor function in very young children (< 2 years) is challenging in view of incomplete myelination in this age group. Few noninvasive tools are available including functional magnetic resonance imaging (fMRI), magnetoencephalography (MEG) and transcranial magnetic stimulation (TMS). MEG and fMRI, primarily localize somatosensory cortex, have a lower success rate, and need sedation in this age group. However, TMS can assess motor cortex by direct stimulation analogous to invasive cortical stimulation and is performed in the awake state. Here we present the results of motor mapping using TMS in children younger than 2 years.

Methods: In a retrospective chart review, we identified children who were under 2 years of age when they underwent TMS for motor mapping as a part of pre-surgical evaluation for either intractable epilepsy or brain tumor. TMS was done while the children are awake and sitting on the lap of caregivers. TMS was applied under MRI guidance to bilateral primary motor cortices while recording electromyography from hand and forearm muscles. The cortical locations where TMS elicited motor evoked potentials and/or cortical silent periods were projected onto the patient’s MRI. MEG under sedation was also done in a subset of these patients for somatosensory mapping. We evaluated the success rates of TMS and MEG.

Results: We identified 28 children (15 males, age range 8 weeks-24 months) who underwent TMS for motor cortex localization. All patients had abnormal structural MRI of brain. A total 36 TMS motor mapping studies were performed in these patients with studies repeated thrice in 2 children and twice in 4. The cortex was visualized at peeling depths of 13-20 mm and the number of TMS pulses ranged from 40 to 343. In all patients, 100% of maximum stimulator output was used and the electric field varied from 150-450 V/m. TMS successfully mapped primary motor cortex of at least one upper extremity in 32/36 studies (89%) and in 24/28 (86%) patients. Both the primary hand cortices were mapped in 25 studies (Figure 1). In two cases where the first attempt was unsuccessful, repeat study 2 to 9 months later was successful. TMS was tolerated well, and one patient had their typical self-limiting seizure after the study was completed. In children with perinatal stroke (n=4) and cortical dysplasia (n=1), TMS was also successful in demonstrating inter-and intra-hemispheric reorganization respectively (Figures 1 and 2). MEG was performed in 14 of these patients and somatosensory cortex could be mapped only in 6 of them (42%) (5 bilateral and 1 unilateral).

Conclusions: In this study, we demonstrate the feasibility of using TMS to accurately localize the motor cortex in very young children who have an immature motor network. TMS is a safe noninvasive tool to map the motor system without using sedation and its success rate appears to be superior to MEG in this age group.

Funding: None
Neurophysiology