Cortical excitability and interhemispheric inhibition after subcortical pediatric stroke: plastic organization and effects of rTMS

Abstract

Objective: Arterial ischemic stroke (AIS) causes disability in children but plastic developmental neurophysiology is unstudied. Imbalance of interhemispheric inhibition (IHI) in adult subcortical stroke is a therapeutic target. We hypothesized that IHI imbalance occurs in childhood AIS and is modifiable by rTMS.

Methods: Eligible SickKids Children's Stroke Program patients included children >7years with subcortical AIS (>2years previous) and functional hand impairment. TMS with electromyography over first dorsal interosseous measured baseline motor cortex (M1) rest and 1mV thresholds and stimulus-response curves (100-150%). Paired-pulse TMS studied bidirectional short (SIHI) and long (LIHI) interval IHI. Children were matched for age/weakness and randomized to contralesional inhibitory rTMS or sham (8days) with measures repeated.

Results: Ten children (mean 13.9 years) had variable weakness (4 mild/2 moderate/4 severe). Stroke M1 motor thresholds were elevated (75±25% versus 55±14%, p=0.05) and decreased with age. Baseline measures suggested excessive LIHI from non-stroke to stroke side (-46±17% versus -28±23%, p=0.08). Following inhibitory rTMS, increases in stroke side maximal MEP amplitudes were suggested and LIHI from stroke to non-stroke side appeared to increase (-20% to -40%). Procedures were well tolerated.

Conclusion: TMS measurement of developmental plastic organization and rTMS interventions are feasible in childhood stroke and IHI imbalance may occur.

Significance: Improved understanding of developmental plasticity after childhood stroke will facilitate better rehabilitational therapy.