The occurrence of mirror movements in children with unilateral cerebral palsy and their typically developing peers using a standardized quantitative assessment: what is normal?

Introduction Mirror movements (MMs) are involuntary movements of one hand that accompany voluntary movements of the other hand. Although they are a physiological feature in typically developing children (TDC), their presence in children with unilateral cerebral palsy (uCP) has been suggested to negatively impact on upper limb function. However, these studies have assessed MMs with anordinal observation-based scale. Here, we used a novel quantitative assessment to investigate the occurrence of MMs in TDC and children with uCP. Patients and methods Eighty-seven TDC (mean age 10y2m, SD 2y4m, 12 left-handed) and 67 age-matched children with uCP (mean age 10y7m, SD 2y4m, 34 left-sided uCP) performed a repetitive unimanual squeezing task making a windmill turn by squeezing a force transducer with one hand while recording force profiles in both hands. MM intensity was calculated as the cross-correlation coefficient between both force profiles. Results Children with uCP showed higher MM intensity than TDC in both hands (MMs in dominant and non-dominant hand, p<0.001). With increasing age, MM intensity slightly decreased in TDC(MMs in dominant hand, rho=-0.28, p<0.05; MMs in non-dominant hand, rho= -0.31, p<0.05), but not in children with uCP. While there was no difference in MM intensity between both hands in children with uCP, TDC showed higher MM intensity in their dominant hand (p