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

Objectives: 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.

Methods: 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.

Results: 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.

Discussion: 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.