What should we do to help children with DCD

See related article on page 608 In this issue of the journal, an important new contribution to the literature on Developmental Coordination Disorder (DCD) explores differences in motor imagery ability in three groups – children with attention-deficit–hyperactivity disorder (ADHD), children with DCD, and children with both conditions. This study provides evidence that DCD has a unique neurological basis, calling into question the notion that ADHD and DCD are merely dimensions of a broader syndrome of generalized developmental deficits. The idea that ADHD and DCD share a common cause has its roots in studies demonstrating very high levels of comorbidity between them: in clinical samples of children with one disorder or the other, 30 to 50% typically prove to have both. This has led to approaches like that of Lewis et al., which seek to explore the common ground these conditions share. By failing to take into account comorbidity between these disorders, previous work may have produced erroneous conclusions regarding underlying mechanisms. A case in point is the association between ADHD and abnormal motor overflow or associated movements. It is not clear whether this relationship is due to impaired inhibition related directly to ADHD or to independent coordination problems. Preliminary evidence currently favours the latter.1 The paper by Lewis et al. poses a similar question. As the authors observe, disrupted motor behaviour may arise from a dysfunction in the neurological networks responsible for motor planning and control, as is thought to be the case with DCD, or from deficits in attention and executive functioning associated with ADHD. In other words, the same impaired performance outcome could arise from functional problems in either of two, quite distinct, systems. This understanding would lead then to the conclusion that similarities in certain clinical features of ADHD and DCD are not necessarily indicative of a common neurological dysfunction or etiology. Lewis et al. examined this hypothesis by building on previous work that has established an internal modeling or efference-copy deficit in children with DCD.2 They explored whether deficits in motor imagery, in this case measured using a guided pointing task, were specific to DCD. By comparing performance in groups of children with ADHD alone, DCD alone, and those with comorbid ADHD and DCD, they demonstrated that this particular deficit occurred predominantly in the DCD-only group. The authors concluded that DCD may be associated with disruption to normal function associated with the inferior parietal lobe. While preliminary, these data support the hypothesis of unique neurological bases for DCD and ADHD. Perhaps most importantly, the method used in this study and others (e.g.1) reflects an important paradigm shift in the field. Only by taking into account comorbid ADHD and DCD can we hope to better understand whether these problems share a common etiology. Motor imagery should be of particular interest to researchers and clinicians in DCD because ‘imagined’ movement shares much of the physiological and neurological apparatus of its ‘real’ counterpart. Some have gone so far as to argue that motor imagery is an internal model of actual movement arising in consciousness simply because the actual movement has been inhibited. It is not surprising then, that children with coordination problems exhibit deficits in imagined movements as well as ‘real’ ones. The clinical implications of this work are intriguing. Previous work from members of this same research team has shown that motor imagery training is as effective as more traditional perceptual motor training in facilitating motor skill development in clumsy children. While the authors note the benefits of this approach in relation to ease of application and convenience relative to traditional physical therapy, there may also be psychological benefits. Children with DCD often report low levels of self-efficacy with regard to their physical abilities, and this lack of confidence may be the principal cause of low levels of participation in sports and other physical activities. These negative self-attributions are also likely to have an impact on ‘training’ to improve motor skill development. Children with DCD learn to conceal their problems by avoiding activities that expose their coordination difficulties and this could limit the effectiveness of skill-development-based interventions. Motor imagery, by contrast, is a safe way of developing skills out of public view. In this sense, its benefits may not be limited solely to physical skill development, but may also be conducive to greater psychological and social well-being.

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