Ipsilesional Motor-Evoked Potential Absence in Pediatric Hemiparesis Impacts Tracking Accuracy of the Less Affected Hand.

Research Report
Population: Pediatric

Jessica Margaret Cassidy, DPT, PhD, Postdoctorate Scholar, University of California, Irvine jmkream@gmail.com

James Carey, PT, PhD, Professor, Department of Physical Medicine and Rehabilitation, University of Minnesota, Minneapolis MN carey007@umn.edu

Linda Krach, MD, President, Courage Kenny Clinical Service Line, Courage Kenny Rehabilitation Institute, Minneapolis, Minnesota linda.krach@allina.com

Tim Feyma, MD, Pediatric Neurologist, Gillette Children’s Specialty Healthcare, St. Paul, MN tfeyma@gillettechildrens.com

Bernadette Gillick, PT, MSPT, PhD, Assistant Professor, Department of Physical Medicine and Rehabilitation, University of Minnesota, Minneapolis, MN gillick@umn.edu

Keywords: Plasticity, Stroke, transcranial magnetic stimulation, pediatric

Purpose: Previous investigation of transcranial magnetic stimulation (TMS)-induced motor-evoked potentials (MEPs) in children and in young adults with congenital hemiplegia confirmed the utility of MEPs in determining corticospinal organization and resultant motor function. The purpose of this study was to analyze the relationship between elicited ipsilesional primary motor cortex (M1) MEPs, finger tracking accuracy, and volume of neural substrate in cortical and subcortical regions of interest on magnetic resonance images (MRIs) in children with congenital hemiparesis. We hypothesized that children showing MEPs would demonstrate significantly higher tracking performance from the affected hand and significantly greater amounts of M1 and posterior limb of internal capsule (PLIC) volume. Subjects: 30 children (13 females) with congenital hemiparesis resulting from arterial ischemic stroke or periventricular leukomalacia aged 8-17 years (mean ± SD = 10.4 ± 2.79 years) Materials/Methods: All participants underwent an anatomical MRI and completed a finger-tracking task wearing custom-made electrogoniometers. Corticospinal excitability was assessed using single-pulse TMS to ipsilesional M1. Participants were divided into two groups based on the presence (n= 19) or absence (n= 11) of an ipsilesional M1 MEP. Investigators blinded to MEP status quantified M1 and PLIC volume and constructed ipsilesional/contralesional (I/C) volume ratios for each region of interest. Finger-tracking performance was analyzed by computing an accuracy index (AI) with higher, positive scores indicative of better accuracy and negative scores indicative of poor tracking response. Two-sample t-tests were performed to assess group (MEP vs. no-MEP) differences in AI scores and M1 and PLIC I/C volume ratios. Results: The MEP group demonstrated significantly greater M1 (p= 0.028) and PLIC (p= 0.005) I/C volume ratios and AI scores from the less affected hand (p= 0.016). AI scores from the affected hand were not significant between groups (p= 0.407). Groups did not differ in age, sex, mirroring, and stroke hemisphere. Conclusions: This study highlights several differentiating factors amongst children with congenital hemiparesis showing contrasting ipsilesional MEP responses: M1 and PLIC I/C volume ratios and less affected hand tracking performance. Clinical Relevance: The above findings pose important clinical implications in pediatric stroke rehabilitation related to the optimization of therapeutic targets and prognostic determination. Our findings of higher tracking performance in the less affected hand of individuals with MEPs with greater PLIC I/C volume are consistent with the phenomenon in the injured developing brain known as “crowding,” whereby preservation of affected hand function occurs at the expense of less affected hand function.

Citation:
Cassidy, Jessica Margaret, DPT, PhD; Carey, James Robert, PT, PhD; Krach, Linda E., MD; Feyma, Tim , MD; Gillick, Bernadette T., PT, MSPT, PhD. Ipsilesional Motor-Evoked Potential Absence in Pediatric Hemiparesis Impacts Tracking Accuracy of the Less Affected Hand.. Poster Presentation. IV STEP Conference, American Physical Therapy Association, Columbus, OH, July 17, 2016. Online. https://u.osu.edu/ivstep/poster/abstracts/061_cassidy-et-al/

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