Waveform-Based Analysis of Head Tremor Using a Marker-Less Tracking Algorithm with 2D-Video: Evaluation of Sinusoidality and Rhythmicity.

BACKGROUND AND OBJECTIVE Tremor is defined as involuntary, rhythmic, and sinusoidal movements. However, differentiating different types of tremors remains challenging due to overlapping features and the subjective nature of clinical evaluations. This study aimed to introduce a novel, video-based waveform analysis to objectively measure two fundamental tremor characteristics, rhythmicity and sinusoidality. METHODS Based on waveforms derived from video-based analysis tracking the patients' nose tip, we defined the coefficient of variation of interpeak intervals (CVIPI) as the measure of rhythmicity index and the slope-fold ratio as the sinusoidality index. For convergent validation, we prospectively enrolled 13 cervical dystonia (CD) patients with head tremor and simultaneously recorded tremor data using both video-based and gyroscope-based methods. Additionally, we applied the algorithm to archived videos of 28 CD and 22 essential tremor (ET) cases with head tremor to analyze individual and group tremor characteristics. RESULTS Video-based indices demonstrated excellent agreement with gyroscope-based measurements for peak frequency (intraclass correlation coefficient [ICC] = 0.99) and the sinusoidality index (ICC = 0.93), while the rhythmicity index showed good reliability (ICC = 0.86). In the application study, CD cases showed significantly lower rhythmicity and sinusoidality than ET cases, forming distinct data-driven clusters between CD and ET. The accuracy of these clusters to the clinical diagnosis was 82.1% and 63.6% for CD and ET, respectively. CONCLUSIONS Video-based analysis of tremor waveforms offers an objective evaluation of rhythmicity and sinusoidality, providing a tool for the objective description of tremor syndromes. Distinct yet overlapping waveform features in ET and CD, analyzed with video analysis, highlight the variability of tremor syndromes. © 2025 International Parkinson and Movement Disorder Society.