Development and Evaluation of Upper Extremity Movement Quality Outcome Measures for Individuals With Functional Movement Disorder

Functional movement disorder (FMD) is a disorder that commonly affects an individual's movement quality; symptoms can range from small tremors to large jerks in the upper extremities. Treatment for FMD is possible, but objective assessments of movement quality are lacking. The goal of this work was to create a movement-quality outcome measure (MOM) that could quantify a range of upper extremity FMD symptoms and compare measures from the literature (for non-FMD patients). Healthy participants were recruited to create hyperkinetic reaching and retrieving movements that emulated four varying FMD symptoms. Four movement-quality outcome measures were calculated, including one developed by the authors: (1) number of peak velocities (NoP), (2) log-dimensionless jerk (LDLJ), (3) spectral arc length (SPARC), and (4) summed centripetal acceleration (SCA). SCA, which was developed by the authors, was created to be able to describe the amount of hyperkinetic movement of the movements as it would be dependent on both the position and velocity profiles. The challenges and benefits of each were assessed based on (1) their correlation with other key aspects of their movement and (2) the ordering of movement type by movement quality. SCA was highly correlated with key outcome measures for three of the geometries (r2 > 0.5) and moderately correlated for one (0.25 ≤ r2 ≤ 0.5), which was greater than any of the other movement-quality outcome measures. This work has the potential to be used in clinical settings to objectively assess an individual's symptoms to track improvements.