Original articleCan Spasticity and Dystonia Be Independently Measured in Cerebral Palsy?
Introduction
Cerebral palsy represents a heterogeneous group of disorders caused by nonprogressive disturbances of the developing brain, leading to dysfunction of movement and postural development [1], [2], [3], [4]. Other impairments (i.e. in sensation, cognition, communication, perception, behavioral, seizure disorder) often accompany the motor dysfunction [1]. The motor disturbances associated with cerebral palsy can range from mild to severe, and may dramatically impair a child’s functional abilities. Children with cerebral palsy frequently have mixed motor disorders (e.g., spasticity, athetosis, ataxia, and weakness), and each likely impairs their functional movement in a different way. Despite the coexisting motor disorders, children with cerebral palsy often fall into one of two classifications: “spastic” or “extrapyramidal” cerebral palsy.
Children with “spastic” cerebral palsy characteristically present with spasticity, weakness, and loss of manual dexterity due to abnormalities in descending motor pathways and motor cortex. Spasticity is defined as increasing resistance to increasing speed of stretch relative to the direction of joint movement or a rapid rise in resistance above a speed or joint position threshold [5]. Spasticity has been widely measured by clinical rating scales (Ashworth scale) [6] and instrumented measures (torque-velocity relationships and velocity-electromyography relationships) [7], [8]. Studies of the degree of spasticity in the lower extremities have not correlated well with aspects of gait function [9].
Dystonia, rigidity, and athetosis are primary neurologic findings of “extrapyramidal” cerebral palsy, presumably a result of abnormalities in basal ganglia-cortical circuits. Dystonia is defined as sustained or intermittent muscle contractions causing twisting and slow repetitive movements or abnormal postures [5]. It can manifest as overflow of activity to muscles that are normally silent during a voluntary movement (e.g., other muscles in that limb or other limbs), or involuntary activation of muscles at rest [10]. Dystonia is often measured clinically in children with cerebral palsy using the Barry-Albright rating scale [11]. As with spasticity, the relatively few published studies describe physiologic measures of dystonia, though some have reported relationships with voluntary movements and walking [12], [13].
Quantitative measures of movement are currently available but have not been widely used. A recent study was the first to describe biomechanical measures that varied in children who were clinically described as having predominantly spasticity vs dystonia [13]. Children with dystonia had greater co-contraction, normal tendon reflexes, and reduced muscle strength all at the knee joint. They also walked with reduced range of knee motion compared with children with spasticity. Thus, preliminary evidence suggests biomechanical measures may be used to distinguish between these types of hypertonicity.
Clinical classifications have been useful in guiding treatments for children with specific motor disorders. However, mixed hypertonia, with components of spasticity and dystonia, is likely to be found in the vast majority of children with cerebral palsy [5]. Identifying the degree to which each motor component contributes to functional movement within an individual is challenging owing to limitations of clinical measurement tools that may be insensitive to small changes in motor performance, and may not specify the mechanism of improvement. With distinct pharmacologic interventions available for different neurologic findings, motor signs, and movements observed in children with cerebral palsy, quantitative measures of motor deficits could provide a more accurate means by which to assess treatments for cerebral palsy [14]. Reported here are relatively simple quantitative measures developed for assessing the motor disorders present in children with “extrapyramidal” and “spastic” cerebral palsy and the extent to which each was found to contribute to the impairments in voluntary arm movements.
Section snippets
Subjects
Thirteen children ages 7 to 17 years, diagnosed with cerebral palsy and subcategorized as spastic vs extrapyramidal (Table 1) were studied. For comparison, eight age-matched healthy control subjects were tested as well. The mean age of the cerebral palsy group was 12 and the control group was 10. No subjects had ever had surgery on the tested upper extremity. One subject (cerebral palsy 10) had Botox to the wrist flexors of the test arm 8 months before testing. Medical history was obtained from
Clinical Scales
All cerebral palsy subjects were assessed using the Ashworth and Barry-Albright scales (Table 1). There was a significant correlation between the Ashworth and Barry-Albright scores (r = 0.68, P = 0.01). This finding suggests that these scales do not necessarily isolate measures of spasticity and dystonia, or that the severity of spasticity and dystonia tend to co-vary in individuals with cerebral palsy.
Spasticity
To measure spasticity in each subject, the slope of the best-fit line in the force vs
Discussion
This study has demonstrated that spasticity and dystonia can be measured in children with cerebral palsy. Our measures correlate with their respective clinical rating scales (Modified Ashworth and Barry-Albright Dystonia scales), suggesting that we are capturing clinically significant elements of these motor signs. Importantly, our measures are not correlated with each other, suggesting some independence of the findings being measured. These tests do not require the child to perform difficult
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