The relation between mirror movements and non-use of the affected hand in children with unilateral cerebral palsy.

AIM: In children with unilateral cerebral palsy (CP), it is widely believed that mirror movements contribute to non-use of the affected hand despite preserved capacity, a phenomenon referred to as developmental disregard. We aimed to test whether mirror movements are related to developmental disregard, and to clarify the relation between mirror movements and bimanual function.

METHOD: A repetitive squeezing task simultaneously measuring both hands' grip-forces was developed to assess mirror movements by using maximum cross-correlation coefficient (CCCmax ) as well as strength measures (MMstrength ). Developmental disregard, bimanual performance, and capacity were assessed using a validated video-observation method. Twenty-one children with unilateral CP participated (Median age 10y 7mo, interquartile range [IQR] 10y 1mo-12y 9mo). Outcome measures of mirror movements were correlated to developmental disregard, bimanual performance, and capacity scores using Spearman's correlations (significance level: α<0.05).

RESULTS

Mirror movements were not related to developmental disregard. However, enhanced mirror movements in the less-affected hand were related to reduced performance (CCCmax : ρ=-0.526, p=0.007; MMstrength : ρ=-0.750, p<0.001) and capacity (CCCmax : ρ=-0.410, p=0.033; MMstrength : ρ=-0.679, p<0.001). These relations were only moderate (performance:MMstrength : ρ=-0.504, p=0.010), low (capacity: MMstrength : ρ=-0.470, p=0.016) or absent for mirror movements in the affected hand. Additionally, seven children showed stronger movements in their less-affected hands when actually being asked to move their affected hand.

INTERPRETATION: These findings show no relation between mirror movements and developmental disregard, but support an association between mirror movements and bimanual function.