Selection and assessment of children with Developmental Coordination Disorder

doi: 10.1111/j.1469-8749.2009. 03372.x Developmental coordination disorder (DCD) is one of the most common childhood disorders, occurring in approximately 5% of the school population. This condition has attracted much interest over the last 35 years and recent research has started to focus on the precise kinematics of the movements seen in these children. Elders et al. suggest that there are three possible levels at which a coordination difficulty might arise in children with DCD: at the most basic level, there may be a difficulty when moving a single degree of freedom (e.g. turning the head); second, there may be difficulty when coordinating two or more degrees of freedom (e.g. moving the head and the arm); or third, there may be difficulty when coordinating with objects in the environment (e.g. reaching out to grasp an object). The Elders et al. study measured the first two of these levels and found that children with DCD displayed atypical movement patterns at even the simplest level. In fact, qualitative observations suggest that the children with DCD had difficulties simply sitting upright and maintaining balance while carrying out the task. This observable deficit in motor control at even the simplest level highlights the difficulties that children with DCD experience. Elders et al. point out that given these observations it is unsurprising that these children perform poorly on standardized assessment tasks where a stable posture must be maintained while synchronizing movement of the hand, arm, and shoulder, for example, the placing pegs task on the Movement Assessment Battery for Children (MABC). The Elders et al. study demonstrated that all aspects of movement in the children with DCD were executed and controlled differently compared with the age-matched control group; this is not an uncommon finding. However, some studies do find a degree of ‘typical performance’ in children with DCD when asked to perform similar motor tasks as the one described in the Elders et al. study. This difference occurs even though studies use similar criteria for assessment of coordination difficulties, i.e. coordination skill below the 5th centile on the MABC and selection in tune with the Leeds consensus statement on DCD. So what causes this difference in performance? Different methods of recruitment could lead to this disparity; the participants in the Elders et al. study were referred by occupational therapists from a local hospital whereas other studies have recruited through family support groups and schools. It has been recognized for some time that recruitment through occupational therapists turns up a very different cohort, in terms of comorbidities and severity, compared with those recruited through schools. Traditionally, the concern has been one of associated difficulties such as attention-deficit–hyperactivity disorder (ADHD) ⁄ attention-deficit disorder (ADD), dyslexia, or Asperger syndrome. Such comorbidities can confound the performance of a child; does a child with a diagnosis of ADHD and DCD display a deficit on a specific motor task because of poor motor skill or because they were not attending to the task? Although I agree that associated difficulties are an issue, I would also like to advocate the importance of considering the severity of the motor difficulty a child experiences. Children recruited through hospitals are likely to fall below the 1st centile; in contrast, children recruited through different avenues may fall slightly higher, at the 4th or 5th centile. If it is acceptable to classify children as simply below the 5th centile then surely we should be seeing similar patterns of both atypical and typical behaviour in children across these studies. The fact that we are not seeing these similar patterns suggests that we should be more careful when grouping children with different levels of severity. However, that is not to say that I believe that careful matching of centile score on assessment test and careful matching of associated difficulties would eliminate variability among a group of children with DCD. One common underlying finding in all studies with DCD is the variability among the clinical group; ultimately the emphasis will always need to be on considering the individual performance of each child with DCD. One final issue that has come out of the Elders et al. study is the validity of standardized assessment tasks. If we accept, as shown here, that many children with DCD have difficulty maintaining basic posture and balance can we assess them alongside a child who can maintain posture and balance and so starts at a different baseline level? Surely we are setting them up to fail before they have even started. Maybe now is the time we moved towards a more precise kinematic assessment of motor abilities, allowing a more comprehensive, and possibly a fairer, description of these individuals.