Exploring Hypertonia in Children With Cerebral Palsy- a Population-based Approach.

A key descriptor associated with the term cerebral palsy is "the disordered development of movement and posture, resulting in activity limitation." The term "movement disorders" is now commonly used to describe a range of observed abnormal movements and postures displayed by children with chronic neurological conditions, of which cerebral palsy (CP) is the most common. These children have muscle tone abnormalities related to non-progressive damage to motor pathways, in particular those contained within the cortex, basal ganglia and thalamus. In recent years there has been much focus on understanding and treating abnormal tone and movements in children with CP, including spasticity and dystonia. Spasticity, which occurs in approximately 90% of children with CP is defined as the velocity-dependent resistance of a muscle to stretch. In general, spasticity is elicited during a standard clinical examination, such as by passive range of joint motion performed at varying speeds.

Dystonia in childhood is defined as ''a movement disorder in which involuntary sustained or intermittent muscle contractions cause twisting and repetitive movements, abnormal postures, or both. ''. In contrast to spasticity, dystonia is inherently more difficult to observe and measure, particularly when spasticity co-exists. When classified according to the dominant form of tone abnormality, it accounts for up to 2-15% of cases. However it is often overlooked in the diagnostic formulation of motor aspects of cerebral palsy, and therefore does not necessarily figure in treatment decision-making. Under-recognised dystonia, when co-existent with spasticity, can produce unpredictable surgical outcomes in the management of gait disorders and associated musculoskeletal deformities. In addition, other abnormal movements such as chorea and athetosis may be observed in these children, adding to the complexity of the movement disorder, but are rarely classified as dominant abnormalities. Improving the recognition of dyskinesias, and situations where they co-exist with spasticity, is important not only for promoting a clearer description of tone and movement abnormalities, but also to help tailor appropriate treatments leading to improved outcomes.

In our recent study describing the motor profiles of 247 5-year-old children in the South Australian CP population, 93.2% of children were coded as primarily spastic-type; 3.2% as dyskinetic (dystonia or athetosis) and 3.6% as ataxic.1 However this study also found that when children were assessed face-to-face by a group of expert paediatricians, 19.4% of the population was noted on observation alone to have abnormal movements, which included dyskinesias. This increased with motor severity by Gross Motor Functional Classification System (GMFCS) from 7% (level I) to 45% (level V). We questioned whether in fact recognition of some dyskinesias are "masked" by the presence of spasticity, according to conventional clinical descriptors. We advocated for the development of a classification system that describes spasticity and dystonia in parallel, to aid the clinician in prescribing treatment strategies. To date no published study has systematically examined for the prevalence of abnormal movements in CP populations, beyond determining the dominant form of tone abnormality in a mutually exclusive fashion, e.g. spasticity or dystonia. Our study proposes a mutually inclusive format using a recently validated tool for the recognition of dystonia and other abnormal movements.