Objective: To develop an objective measure for a dystonia subtype called cervical dystonia (CD) using a commercially available wearable sensor technology.

Background: CD is a disabling brain disorder manifested by abnormal neck postures with limited efficacy from current treatments. A barrier to measuring treatment efficacy is that current clinician-rated outcome measures show high inter-rater variability, and poor sensitivity. Newer software-based measures offer an opportunity to bypass these limitations. Recent proof of feasibility studies in dystonia have demonstrated that wearable sensor and video capture-based methods associate with clinician-rated scales and patient-reported outcomes. Uncertainties, however, remain about the best way to derive and analyze these sensor and video capture-based measures of dystonia.

Method: 16 healthy volunteers (HV) and 21 CD subjects completed a single observational visit. CD inclusion criteria were subjects at least three months from their neurotoxin treatment or with their deep brain stimulation device in the off state. HV exclusion criteria were any abnormal neck postures. During the visit, all subjects wore an inertial measurement unit (IMU) device on their head and neck. Subjects performed a fixed pattern of neck movements in three axes: flexion-extension (FE), lateral-flexion (LF), and neck rotation (NR) for five trials. The IMU captured the x, y, z coordinates and time at a sampling frequency of 200 Hz, which was automatically converted to angles over time.

Results: HV and CD showed no significant differences in age (-6.28 years, p= 0.0986, t-test), or sex (p= 0.733, Fisher’s exact test). To derive measures of neck movements, angles over time data for each subject and axes were used to calculate four kinematic measures:  angular velocity (angle/s), acceleration (angle/s²), jerk (angle/s³) and frequency (1/s). The peak sum of each kinematic measure that was one standard deviation above the mean for that trial was then calculated. This approach allowed us to derive a sum for each kinematic measure per trial per axis for each subject.

Conclusion: Our study uses a consumer accessible wearable sensor device to derive kinematic measures of neck movements. Findings from this study can be used to develop quantitative objective measures of dystonia to use as a tool in clinical and research settings.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/cervical-dystonia-objectively-measured-with-wearable-sensor-system/