Mirror movements in children with unilateral cerebral palsy due to perinatal stroke: clinical correlates of plasticity reorganization.

AIM: We aimed to determine if the mirror movements that often result in children with unilateral cerebral palsy (CP) after perinatal stroke represent a clinical biomarker of developmental plasticity.

METHOD: This was a prospective, controlled cohort study. Mirror movements in children with unilateral CP from a population-based cohort were compared to those of typically developing controls. The population with stroke was assessed further via electromyography (EMG), motor function, and corticospinal organization investigations. Mirror movements were quantified (0-5) bidirectionally. EMG mirror movements were quantified during voluntary contraction. Motor function was quantified by validated measures including the Assisting Hand Assessment (AHA). Corticospinal organization was categorized as ipsilateral or contralateral using transcranial magnetic stimulation (TMS). The relationships between mirror movements, function, and corticospinal organization were assessed (t-tests, Pearson rank correlation coefficients).

RESULTS: Ninety-two participants were scored (55 males, 37 females, mean [SD] 12y [5y 6mo], range 4-17y), 63 with complete motor outcomes and 39 with TMS data. EMG ratios correlated with clinical mirror movements (r=0.562, p=0.008). Mild mirror activity in controls declined with age (r=-0.459, p<0.001). Mirroring was stronger with tasks performed by the affected hand (p<0.001). Mirror movements correlated with AHA scores (r=-0.255, p=0.04) and poor motor outcome (p<0.001). Unaffected hand mirror activity was higher in children with ipsilateral corticospinal tract arrangements (p<0.001).

INTERPRETATION: Clinical mirror movements correlate with disability and corticospinal organization in children with unilateral CP with perinatal stroke. This simple bedside biomarker could facilitate patient selection for personalized rehabilitation.

WHAT THIS PAPER ADDS: Mirror movements are a clinical indicator of corticospinal organization in children with unilateral cerebral palsy with perinatal stroke. Mirroring is strongest in children with ipsilateral corticospinal tract reorganization. The concept of a 'directionality factor' to mirror movements highlights additional, clinically relevant functional correlations.