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Reliability of the kinematic dystonia measure (KDM) in children with upper extremity dystonia


1. Bloorview Research Institute, Bloorview Kids Rehab, Toronto, ON, Canada;
2. Department of Paediatrics, University of Toronto, Toronto, ON, Canada;
3. McMaster University, Hamilton, ON, Canada.

Background/Objectives: Children with cerebral palsy (CP) and acquired brain injury (ABI) frequently present with dystonia. Dystonia is defined as a movement disorder in which muscle contractions cause repetitive movements and twisting or abnormal postures. The Kinematic Dystonia Measure (KDM) is a tool that quantifies the amount of involuntary movement in a dystonic upper extremity. Preliminary evidence suggests that it correlates well with clinical measures currently used to evaluate dystonia. The purpose of this study is to obtain data on the test-retest reliability and construct validity of the KDM.

Design: Case control with prospective repeated measures.

Participants and Setting: 11 children (9 years, SD 1 year 6 months) with upper extremity dystonia secondary to CP or ABI (>2 years prior to study) were recruited from a tertiary care centre for children with physical disabilities. Six typically developing subjects (8 years 3 months, Sd 2 years 11 months) were recruited as controls.

Materials/Methods: The KDM measures involuntary translational and rotational movement of an affected upper limb while the individual taps their contralateral hand at a rate of 175 beats per minute using an auditory cue. Three-dimensional joint positions and angular rotation of the shoulder, elbow and wrist were sampled at 120Hz using a Vicon MX motion capture system. To obtain reliability data, subjects were tested twice with the KDM at least 30 minutes apart. Prior to testing, the Barry Albright Dystonia scale (BAD) was completed for each subject.

Results: KDM results for the subjects (168.64 0 ± 100.82 0) showed significantly more involuntary movement than controls (50.94 0 ± 31.59 0) (p=0.007) (Figure 1). KDM measurements also correlated with BAD scale results (Spearman R 0.80, p=0.003). The intraclass correlation coefficient (ICC) for KDM measurements in the subjects was 0.95 (95% CI 0.99, 0.82).

Conclusions/Significance: In this study, KDM measurements were significantly higher in children with upper extremity dystonia compared to controls. Increased KDM scores correlated well with increased severity of dystonia as measured by the BAD Scale. Both of these findings support the validity of the KDM. Importantly, the KDM also showed excellent test-retest reliability. This is a key finding given that a hallmark feature of dystonia is variability. The above three findings support the potential use of the KDM as an evaluative measure that is able to quantify changes in dystonia in the pediatric population. Future studies evaluating test-retest reliability over a longer timeframe are planned.

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