Characterization of multi-joint upper limb movements in a single task to assess bradykinesia.

Bradykinesia is a disabling symptom of Parkinson's disease (PD) which presents with slowness of movement. Visual assessment using clinical rating scales is currently the gold standard to assess bradykinesia. Such assessments require multiple separate movements, are subjective, and rely on the ability of the rater to determine frequency and amplitude features of excursion of multiple joints simultaneously. The current study introduces the use of wearable inertial measurement units (IMUs) to characterize full-arm repetitive movements and provide a new index score for bradykinesia severity (BKI) in the upper limbs. The BKI provides an approach to measuring bradykinesia reliably and objectively. Importantly, this index is needed to demonstrate separability between healthy individuals and PD participants, and also between bradykinetic and non-bradykinetic PD participants. Thirteen PD participants and ten age-matched healthy control participants were studied. Using a single upper limb task that activated multiple joints and recordings from angular displacements from all joints, features relevant to demonstrating bradykinesia were extracted and systematically combined to create the total BKI. A strong correlation coefficient was obtained comparing BKI to upper limb UPDRS bradykinesia scores (rs=-0.626, p=0.001). The BKI successfully identified differences between control and PD participants (p=0.018). The BKI was also sensitive enough to identify differences within the PD population, separating PD participants with and without bradykinesia (p<0.001). This study demonstrates the feasibility of using IMU-based motion capture systems and employing the new BKI for quantitative assessment of bradykinesia. This approach when generalized to lower extremity and truncal movements would be able to provide an objective and reproducible whole body bradykinesia index.