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.