Objective: To develop a quantitative and objective tool to track repetitive tapping movement (RTM) using a slow motion capture and compare patients with Parkinson’s disease (PD), REM-sleep behaviour disorder (RBD) and healthy controls (HC).

Background: Bradykinesia is the defining motor feature of PD. There are considerable limitations in their assessment using standard clinical rating scales, which are semiquantitative introducing some inter-rater variability, and subtle changes in the early stages of PD can be difficult to detect.

Method: This is a cross-sectional study of 48 participants (PD=20, RBD=5, HC=23). For each participant, RTM was recorded during 20s using a smartphone at 240 frames/s and then analysed using novel Python scripts. Clinical assessment was based on the motor score of MDS-UPDRS. Two kinetic parameters were extracted: amplitude between fingers and frequency (number of taps/s). Linear regression was used to determine trends over time.

Results: Despite the HC and RBD groups being significantly older than the PD group (64.8±8.7yo, 68.4±8.2yo and 58.1±12.8yo, respectively, p=0.001), the PD group performed the task significantly more slowly (p=0.0003). The RBD group was similar to the PD group with significantly slower RTM compared to controls (p<0.0001). No difference in amplitude decrement was found between the groups. The frequency parameter SMART test was able to differentiate between groups PD vs HC and RBD vs HC, demonstrating 93% and 100% of sensitivity for 61% and 87% specificity respectively. The respective AUCs were 0.84 and 0.92.

Conclusion: We present a novel method to quantify motor dysfunction in PD. In particular, frequency appears to be a sensitive parameter to differentiate between patients and controls. Despite the small number of subjects, the RBD group had detectable difference in motor function, which could help with early diagnosis in the prodromal phase of PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/slow-motion-analysis-of-repetitive-tapping-smart-test-a-new-means-to-assess-bradykinesia/