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Motor impairment in Attention Deficit Hyperactivity Disorder (ADHD); part of the ADHD phenotype?

Sat, March 23, 9:45 to 11:15am, Hilton Baltimore, Floor: Level 1, Latrobe

Integrative Statement

Introduction
A co-occurring motor impairment is evident in children with ADHD, with ~50% meeting the criteria for Developmental Coordination Disorder (DCD). Despite this, few studies have investigated the motor system in ADHD and it is currently unclear whether a motor deficit is a characteristic of ADHD itself, or whether it reflects a co-occurring motor deficit distinct from ADHD symptomology. Here we present findings from a battery of motor tasks from a large group of children with ADHD, with two aims. Aim 1: to present the most comprehensive report of the motor profile in ADHD to-date. Aim 2: to address whether a motor deficit is inherent to ADHD.
Hypotheses
1. The ADHD group will present with an uneven profile of motor impairments. The syndrome-specific profile, however, might be a feature of a subgroup of children with ADHD who show a generalised motor impairment only.
2. If the motor impairment is inherent to ADHD, this predicts an association between ADHD core characteristics and motor performance. If a motor impairment in ADHD represents a subgroup of children, this predicts no such association.
Study population
Participants with ADHD (N=52) and typically developing (TD) motor matched control children (N=75)
Methods
Participants completed the largest battery of assessments of motor function that have been used with this population to-date. This comprised of the Bruininks-Oseretsky Test of Motor Proficiency Second Edition (BOT2; Bruininks & Bruininks, 2005), a Wii balance board postural sway task, and a finger-thumb task (touching the thumb to each finger in turn repeatedly). We also included a parent-report measure of motor milestone achievement. To measure ADHD core characteristics, parents/caregivers completed questionnaires relating to ADHD symptomology (Conners’ Parent Rating Scale [Conners, 1997], Child Behavior Checklist [Achenbach & Rescorla, 2001], Strengths and Difficulties Questionnaire [Goodman, 1997], and participants completed a behavioral measure of inhibition (Go/No Go task).
Results
A motor deficit was observed in 44% of our ADHD sample. This deficit did not represent a simple delay in development; rather, there was an uneven profile of motor performance across different motor tasks, relative to TD children. Interestingly, even those children with ADHD who displayed a typical level of overall motor ability (ADHD-H), exhibited the same uneven profile, albeit attenuated relative to those with ADHD and low motor ability (ADHD-L).
Few relationships were observed between ADHD core characteristics and motor competence. We also found that the ADHD-L group was not delayed in reaching motor milestones (e.g., crawling and walking) as infants. This suggests that the motor deficit present in some children with ADHD results from subtle impairments in infancy (perhaps in attention), which impact later motor development. It is possible that protective factors or compensatory strategies attenuated this developmental cascade in the ADHD-H group; this is supported by the similar motor profile for both ADHD-L and ADHD-H groups.
We conclude that whilst a motor impairment is not related to ADHD core characteristics, it is a developmental consequence of ADHD (rather than a completely unrelated co-occurring deficit) which impacts some but not all children with ADHD.

Authors