Clinical Utility of Transcranial Magnetic Stimulation (TMS) in the Presurgical Evaluation of Motor, Speech, and Language Functions in Young Children With Refractory Epilepsy or Brain Tumor: Preliminary Evidence

Abstract

Accurate presurgical mapping of motor, speech, and language cortices, while crucial for neurosurgical planning and minimizing post-operative functional deficits, is challenging in young children with neurological disease. In such children, both invasive (cortical stimulation mapping) and non-invasive functional mapping imaging methods (MEG, fMRI) have limited success, often leading to delayed surgery or adverse post-surgical outcomes. We therefore examined the clinical utility of transcranial magnetic stimulation (TMS) in young children who require functional mapping. In a retrospective chart review of TMS studies performed on children with refractory epilepsy or a brain tumor, at our institution, we identified 47 mapping sessions in 36 children 3 years of age or younger, in whom upper and lower extremity motor mapping was attempted; and 13 children 5–6 years old in whom language mapping, using a naming paradigm, was attempted. The primary hand motor cortex was identified in at least one hemisphere in 33 of 36 patients, and in both hemispheres in 27 children. In 17 children, primary leg motor cortex was also successfully identified. The language cortices in temporal regions were successfully mapped in 11 of 13 patients, and in six of them language cortices in frontal regions were also mapped, with most children (n = 5) showing right hemisphere dominance for expressive language. Ten children had a seizure that was consistent with their clinical semiology during or immediately following TMS, none of which required intervention or impeded completion of mapping. Using TMS, both normal motor, speech, and language developmental patterns and apparent disease induced reorganization were demonstrated in this young cohort. The successful localization of motor, speech, and language cortices in young children improved the understanding of the risk-benefit ratio prior to surgery and facilitated surgical planning aimed at preserving motor, speech, and language functions. Post-operatively, motor function was preserved or improved in nine out of 11 children who underwent surgery, as was language function in all seven children who had surgery for lesions near eloquent cortices. We provide feasibility data that TMS is a safe, reliable, and effective tool to map eloquent cortices in young children.

Neurosurgery for eloquent lesions in children: state-of-the-art rationale and technical implications of perioperative neurophysiology

“…16 Thus, pediatric cases per se requiring awake intraoperative mapping and resection may now receive comparable mapping and care by extraoperative mapping even in rather young children. 13,16 In line with our own experience, nTMS was reported to provide reliable data in patients as young as 4 to 6 years of age for language function. 13,14 Mapping functions other than motor and language have been established as well.…”

“…13,16 In line with our own experience, nTMS was reported to provide reliable data in patients as young as 4 to 6 years of age for language function. 13,14 Mapping functions other than motor and language have been established as well. 24,25 Apart from exclusive mapping approaches, repetitive nTMS allows for the treatment of postoperative deficits.…”

Presurgical language mapping in bilingual children using transcranial magnetic stimulation: illustrative case

“…In our case, we instead simplified the stimuli used in the Italian study to include only basic colors and numbers (1–10), so that we could easily learn the correct responses, provided by the patient’s mother in order to ensure accuracy and correct for dialectal characteristics, for analysis. Although we have had success using color-naming tasks for clinical language mapping in young and developmentally delayed children, 39 it is possible that the more rote number-naming task utilized a different network entirely, as recent direct cortical stimulation findings suggest. 40 Indeed, our patient made no errors when presented with number stimuli during stimulation, and thus we do not recommend use of number-naming tasks for TMS language mapping.…”

Plasticity in the developing brain: neurophysiological basis for lesion-induced motor reorganization

“…Longitudinal and cross-sectional neurophysiological studies of typically developing infants and children are likewise consistent with the withdrawal of uncrossed corticospinal axons over the first 24 postnatal months, such that ipsilateral motor evoked potentials (MEPs), like those elicited by transcranial magnetic stimulation (TMS), are less frequent, smaller, later in onset and have higher thresholds compared to contralateral muscle responses at 2 years of age. 11 , 15 …”