Bilateral multi-condition surface electromyographic characterization of tremor in Parkinson's disease and essential...

Clinical differentiation between Parkinson's disease (PD) and essential tremor (ET) remains challenging, particularly in early or overlapping cases. This study aimed to characterize bilateral tremor features using multi-condition surface electromyography (sEMG) and to evaluate task-dependent modulation patterns relevant to differential diagnosis.

Thirty patients with PD and forty-one with ET underwent bilateral sEMG recordings from agonist-antagonist muscle pairs. Tremor frequency, burst duration, amplitude, and activation patterns were systematically analyzed under four functional conditions: rest, posture, object holding, and weight loading. Between-group and within-group comparisons were performed.

Across all task conditions, tremor frequency was significantly higher in ET than in PD. Tremor frequency was lowest at rest; within-group modulation differed between disorders, with ET showing a significant rest-posture difference and PD showing lower resting frequency than active conditions. ET predominantly showed synchronous agonist-antagonist activation and more homogeneous burst duration distribution, whereas PD was characterized by asynchronous activation and greater heterogeneity in burst duration. Bilateral recordings revealed no significant inter-lateral electrophysiological differences in either disorder, compatible with a predominantly central contribution to tremor generation.

Bilateral multi-condition sEMG analysis demonstrated task-dependent tremor modulation and differences in agonist-antagonist activation patterns between PD and ET. This electrophysiological approach may complement clinical assessment, particularly in cases with overlapping tremor phenomenology.