By: John Cairney, Scott Veldhuizen and Peter Szatmari
Introduction
There has been clinical interest in children who present as clumsy or physically awkward for some time [1]. Until about a decade ago, research in this area was fragmented by the absence of consensus on how best to describe and define this disorder – a nosological problem that is not uncommon in psychiatry. In some areas, researchers considered, and still consider, motor coordination problems in children principally as a feature of broader syndromes such as ‘deficits in attention, motor control, and perception’ (DAMP; [2]) or, previously, ‘minimal brain dysfunction’ [3]. Although problems with motor coordination may be a feature of many different disorders, or may represent part of the normal continuum of functioning, it is now widely recognized that significant motor problems may occur independently of other conditions and should be a separate focus of identification and treatment.
In 1994, an international group of experts agreed to adopt the label ‘developmental coordination disorder’ (DCD) to describe poor motor performance of unknown cause [4], adopting a term and definition which had already been included in the 3rd edition of the Diagnostic and Statistical Manual of the American Psychiatric Association (DSM) [5]. These criteria were retained in DSM-IV [6], and also appear, with minor changes, in the preliminary draft revisions for DSM-V ([7]; Table 1). DCD is defined, essentially, as the presence of motor coordination problems that interfere significantly with functioning and are not due to a pervasive developmental delay or medical conditions such as cerebral palsy or muscular dystrophy.
In this paper, we briefly discuss issues of measurement and case ascertainment still relevant in DCD research, and then review studies on the co-occurrence of DCD and other psychiatric disorders in children. This is an area of significant active research, and one that touches on important issues in the field, notably the cause of DCD, and whether it should be considered an independent disorder at all. We discuss conditions that have been shown to be frequently present in children with motor skill deficits, but not those (such as pervasive developmental delay, autism spectrum conditions, or schizophrenia) that may include motor delay or motor coordination problems as a feature of the disorder or a side.
Recent findings
Although a general consensus on the disorder definition exists, case identification in research studies remains problematic. Despite this, recent research has reported high levels of attention deficit/hyperactivity disorder and internalizing disorders among children with poor motor coordination. These findings offer some support for the longstanding view that DCD may be one facet of a broader syndrome that includes learning difficulties and deficits in attention. ‘Pure’ cases are common, however, and other work suggests that DCD and attention deficit/hyperactivity disorder have distinct causes. There is also some evidence that internalizing disorder may be a consequence of DCD.
Summary
Measurement issues in DCD persist, whereas findings on comorbidity have both illuminated the nature of the disorder and heightened debate on its usefulness as a distinct diagnostic entity.
Keywords
anxiety, attention deficit hyperactivity disorder, children, comorbidity, depression, developmental coordination disorder, disability, internalizing disorders, internalizing problems effect of treatment. We generally use the term ‘motor coordination problems’ when discussing studies that did not apply full diagnostic criteria for DCD.
Measurement issues in developmental coordination disorder research
DCD is thought to affect 5–6% of children [6]. Agreement on the approximate prevalence is not universal, however. Although standardized assessments of motor problems have enabled researchers to consistently identify children with poor motor skills, the promotion of the 5% prevalence estimate has led to the somewhat tautological use of the 5th percentile on these assessments as the cut-point for significant motor impairment.
One recent prevalence study that attempted to stringently apply the impairment requirement (criterion B) found that only 1.7% met full diagnostic criteria [8_].
Although the rigorous application of diagnostic criteria may increase the accuracy of prevalence estimates, two related and nontrivial problems remain. Lingham et al.[8_] still had to select a cut-point for motor performance, which highlights the thorny issue of exactly how much impairment is required to fulfill that criterion: motor coordination represents a spectrum of functioning, and any threshold used to identify disorder’ will have its own set of costs and benefits [9]. This question has not yet been fully resolved, although attempts have been made to better define impairment in the context of the disorder [10].
In population-based studies, there are also important practical issues in the assessment of DCD. Combining multiple criteria may, depending on the level of error associated with each, actually increase error and reduce diagnostic accuracy [11], especially when the base rate for the disorder is low. It is also difficult and costly to conduct full neurological assessments to rule out other pathologies [12], and fully evaluating impairments in functioning can be similarly problematic. One effect of measurement difficulties is that, despite the existence of a consensus diagnosis, myriad related terms (‘physical awkwardness’, ‘developmental motor delay’) continue to be used – as in the present paper – by researchers reluctant to describe motor coordination problems as DCD when full disorder criteria have not been applied.
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