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

Abstract

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.

Importance of assessing the intermanual asymmetry of mirror movements in paediatric hemiparesis

“…However, excessive presence, persistence, or reappearance of mirror movements are a biomarker of atypical development or lesion of the motor system's organization . Riddell et al conducted a study of mirror movements combining behavioural and neurophysiological assessments (with clinical tests, electromyography, and transcranial magnetic stimulation [TMS]) in a large cohort of hemiparetic children with well‐characterized unilateral cerebral palsy due to stroke. In line with previous findings, the authors show that a large amount of mirror movements predicts poor manual function.…”

“…Riddell et al also highlight that intermanual asymmetry of mirror movements is a valuable biomarker. Asymmetry is not systematically found in all participants, but when it is, children present more mirror movements on the non‐paretic hand when the task is performed by the paretic hand than conversely . There is no unique model explaining the asymmetry of mirror movements and its directionality.…”

“…However, in the case of hemiparesis, another hypothesis is that the non‐paretic hand would produce more mirror movements as a sort of compensatory mechanism devoted to assist voluntary movement of the paretic hand, especially in children with poor motor outcome . Beyond this functional hypothesis, Riddell et al provide a new neurophysiological account for asymmetry of mirror movements by showing that only children with asymmetrical mirror movements present an ipsilateral organization of the corticospinal tract (assessed by TMS). In these children, stronger mirroring in the non‐paretic hand may result from an abnormal persistence of ipsilateral corticospinal tract from the damaged hemisphere, in addition to the crossed corticospinal tract from the undamaged hemisphere …”

“…Thus, the results of Riddell et al offer clues to understand the heterogeneity of mirror movements manifestations in unilateral cerebral palsy by distinguishing two profiles: (1) children with symmetric mirror movements, non‐ipsilateral corticospinal tract, and good motor outcome; and (2) children with asymmetrical mirror movements, ipsilateral corticospinal tract, and poor motor outcome. A link between the profile and the type, timing, location, or size of lesion remains to be determined . Moreover, longitudinal multimodal studies are required to understand the ipsilateral organization.…”

“…Particularly, the possible atypical development of transcallosal inhibitory connections between the undamaged and damaged hemispheres could prevent age‐related inhibition of mirror movements of the non‐paretic hand . Otherwise, even if asymmetry was found irrespective of the task (tapping, sequencing, grasping), it would be interesting to investigate how task parameters such as force or speed, could modulate the asymmetry of mirror movements for each profile …”