Neuropsychological function in children with primary complex motor stereotypies

Stereotypies are rhythmic, repetitive, fixed, predictable, but purposeless movements that stop with distraction. They occur in children who are otherwise developing typically (primary), as well as in those with underlying neurological conditions (secondary). Complex motor stereotypies (CMS) include repetitive bilateral movements, typically affecting the arms, hands, and fingers (e.g. flapping, waving, wiggling) and are occasionally accompanied by facial distortions, neck extension, and a vocalization. 1 Primary CMS are diagnosed when CMS are observed in an individual with otherwise typical development, i.e. not in the context of autism spectrum disorders (ASDs), Rett syndrome, or blindness or other sensory deprivation. Primary CMS typically appear before the age of 3 years1 and have a persistent course.2,3 Episodes of CMS last for periods of seconds to minutes, occur in clusters, and may appear many times per day. They are associated with periods of excitement, engrossment, stress, fatigue, and/or boredom, and are readily suppressed by sensory stimuli or distraction. Common comorbidities, based on parent report, for children with primary CMS include attention-deficit–hyperactivity disorder (ADHD; ~30%), tics (~18%), and obsessive–compulsive behaviours (~10%).2 Aetiologically, a positive family history of CMS has been identified in 25% of families with a child with CMS.2 Differential diagnoses include complex motor tics, compulsions, and paroxysmal dyskinesias.4 Pathophysiological hypotheses have also included both psychological causes and abnormality of motor control.5,6 A recent electrophysiological study of children with primary CMS found that, unlike voluntary movements, CMS were not preceded by premotor movement-related cortical potentials, suggesting that stereotypies use different pathways from those involved in voluntary movements.7 Anatomically, motor stereotypies are believed to involve cortico-striatal-thalamo-cortical circuitry and it is likely that they alter synaptic neurotransmission. 8 Recent research, including animal models of CMS, has suggested that distinct frontostriatal pathways underlie habitual and goal-directed behaviours, such that premotor–putamen circuitry is associated with habitual behaviours, while ventromedial prefrontal–caudate pathways are associated with reflective goal-directed activity.9 Although descriptive studies of the phenomenology of primary CMS have increased,2,5,10–12 it remains unclear whether children with CMS manifest neuropsychological dysfunction beyond atypical movements. Hence, the goal of the present study was to examine behavioural and neuropsychological function in a large sample of well-characterized children with primary CMS, and to compare their performance with that of age- and sex-matched comparison children with typical development. Given the preliminary findings from neuroimaging, electrophysiological studies, and animal models, it was hypothesized that children with primary CMS would manifest behavioural deficits in functional skills associated with cortico-striatal-thalamo-cortical (especially premotor–putamen) circuitry, thus affecting motor and executive control. A secondary goal was to assess the construct validity of two-dimensional parent report measures of stereotypy severity (i.e. the Stereotypy Severity Scale [SSS] and the Stereotypy Linear Analog Scale [SLAS]), as related to neurobehavioral function. It was further hypothesized that stereotypy severity would be significantly associated with neuropsychological dysfunction.