Cerebral lateralization and functional outcome in neonatal brachial plexus palsy

Slower handwriting performance may be related to altered motor planning, bimanual coordination, fine motor automaticity, and cognitive processes. The cross-sectional study conducted by De Pauw et al. on reduced handwriting speed in left-handed children after neonatal brachial plexus palsy (NBPP) provides valuable insights regarding the influence of cerebral lateralization in this population.1 The authors found that left-handed individuals with right-sided NBPP had reduced handwriting speed compared to controls. Aligning with findings of unique motor control architecture in converted left-handed individuals,2 these findings draw us to consider whether neuroplastic changes influence handwriting performance in left-handed children after right NBPP. Although this work furthers our understanding of the complex interplay between cortical, peripheral nerve, and orthopaedic sequalae on functional outcome, these findings must be interpreted alongside a few methodological considerations. The cognitive outcomes reported in this study should be interpreted within the context that the derived IQ was generated from the Wechsler Intelligence Scale for Children, Third Edition (WISC-III) short form (block design, picture completion, vocabulary, and similarities subsets). Although WISC-III short forms have strong reliability to the full test, caution is advised in interpreting these findings as proxy for an IQ. Most children with NBPP have typical cognitive functioning although children with more severe NBPP may have associated developmental and language delays.3 In the study by De Pauw et al., half of the NBPP cohort were classified as Narakas 3 and 4, indicating total plexus injuries. Therefore, neurodevelopmental changes related to birth trauma and severity of NBPP may have contributed to low derived IQ outcomes. Severity of NBPP also has implications on handwriting speed and motor/dexterity outcomes. For example, use of the affected limb to stabilize the paper while handwriting is a critical factor during a timed task. Further, there is evidence that children with NBPP may have balance and postural deficits.4 Overall, the potential impacts of the severity of impairment in the non-dominant (i.e. NBPP affected hand) and postural control on reduced handwriting speed should not be ignored. Additionally, De Pauw et al. included a wide age range (6–21 years) of participants with NBPP and controls. Significant variability in handwriting performance and fluency occurs with age as language, visual motor, fine motor, and executive functioning skills develop in childhood and adolescence. To address the age-related developmental differences, it is important to include normative handwriting data across the spread and matched comparison of these outcomes. For example, the discrepancy in handwriting speed is more apparent in the younger age group compared to the older age group. These findings could be attributed to developmental differences in areas such as visual motor integration and fine motor abilities. Pain is also an important factor in understanding handwriting and motor/dexterity outcomes, as children with NBPP may experience upper limb pain.5 Although varying in severity and frequency, the pain is described as musculoskeletal or neuropathic in nature. In their study, only one participant experienced pain and pain outcomes were reported in only 14 of the 32 participants with NBPP. Pain in the affected limb and/or from overuse of their unaffected side may influence functional performance, including handwriting and timed tasks. De Pauw et al.'s study advances our understanding of the potential role of cerebral lateralization on functional outcome in children with NBPP. The methodological issues related to the impacts of NBPP severity, pain, and age/developmental stage on outcomes of handwriting speed are important to consider when interpreting these findings. Their work highlights that future research on cerebral lateralization after NBPP that investigates covariates such as pain, severity of injury, and cognitive/language functioning on outcomes of unilateral tasks with this population is needed. Not required.