Movement disorders in childhood are characterized by a heterogeneous variety of difficulties. One of the common movement problems, but often misidentified and/or under-diagnosed, is motor stereotypies. Differentiating motor stereotypies from other movement problems (such as tics) can be difficult. According to the DSM-5, stereotypies are ‘repetitive, seemingly driven, and non-functional motor behaviors’, but the clinical presentation can vary from more simple movements like rocking and head banging, to more complex presentations like hand and arm flapping. When these stereotypies interfere with normal activities and are present for a minimum of 4 weeks, a diagnosis of stereotypic motor disorder (SMD) is given. However, motor stereotypies often occur in the presence of other conditions, like autistic spectrum disorders, developmental delay, Rett syndrome, and blindness; but also attention-deficit-hyperactivity disorder (ADHD) and obsessive compulsive disorder (OCD). These stereotypies are called secondary motor stereotypies and this group represent the largest proportion. Good clinical practice of the assessment of motor stereotypies must encompass not only a thoroughly neurological evaluation, but also a psychiatric and psychosocial screening. The presence of motor stereotypies in the absence of other conditions, called primary motor stereotypies, has been estimated to occur in up to 7% of children. In recent years, knowledge about the phenomenology of primary motor stereotypies has increased. However, some important and fundamental questions remain.
According to the DSM-5, SMD is classified in the category of neurodevelopmental disorders, suggesting a neurobiological underpinning. Although the underlying neurobiological pathway is not fully understood, there is evidence that the frontostriatal circuit is affected. It is known that other conditions in which the frontostriatal pathway is involved (like ADHD, tic disorders, and OCD) are marked by neurocognitive problems. Therefore, it is clinically and scientifically relevant to investigate whether children with primary motor stereotypies demonstrate neurocognitive problems, similar to the cognitive problems seen in other neurodevelopmental disorders.
In the paper by Mahone et al., a first step has been taken in investigating the neuropsychological profile of children with primary motor stereotypies. The results demonstrate that children with primary motor stereotypies have a largely intact neurocognitive profile, but a positive association was found between frequency and severity of motor stereotypies and parent reports of attentional and executive difficulties. Additionally, a substantial proportion of the children were rated as having motor skill difficulties consistent with developmental coordination disorder. These findings suggest screening for more subtle and less overt problems is warranted.
Motor stereotypies are visible and can overshadow the presence of more subtle cognitive and/or motor problems that interfere with daily functioning. Future research needs to expand the broader phenomenology of primary motor stereotypies, including neurocognitive and motor functioning. Additional imaging studies are required to test the frontostriatal hypothesis. The neurobiological model has gained more credibility over the years, but it is a clinical and scientific pitfall to ignore psychosocial factors. There is evidence that motor stereotypies can be triggered by psychosocial factors (e.g. excitement, being focused, anxiety, or fatigue) and motor stereotypies can acquire a functional value, e.g. regulation of arousal.
Interference with daily functioning is one of the criteria in the DSM-5 for diagnosis of SMD. Despite this criterion, it is unclear to what extent stereotypies (can) interfere with daily functioning. Additionally, little is known about the impact of primary motor stereotypies on the well-being and quality of life of the child.
Clarifying these issues is crucial in establishing the most appropriate treatment of motor stereotypies and some progress has been made in recent years. To date, some evidence exists for the beneficial effect of two behavioral techniques: habit reversal and differential reinforcement of other behaviors. To date, pharmacological treatment has had no therapeutic effect. Interestingly, habit reversal has also proven to be effective in the treatment of tic disorders.
The research field of motor stereotypies has revealed important insights, but many challenges still need to be addressed. Currently, a solid conclusion for practitioners is that the diagnosis and treatment of motor stereotypies require an interdisciplinary approach.