Usefulness of intermuscular coherence and cumulant analysis in the diagnosis of postural tremor

Objective: To investigate the potential value of two advanced EMG measures as additional diagnostic measures in the polymyographic assessment of postural upper-limb tremor. Methods: We investigated coherence as a measure of dependency between two EMG signals, and cumulant analysis to reveal patterns of synchronicity in EMG activity in muscle pairs. Eighty datasets were analyzed retrospectively, obtained from four groups: essential tremor (ET), Parkinson's disease (PD), enhanced physiological tremor (EPT), and functional tremor (FT). Results: Intermuscular coherence was highest in the PD group (0.58), intermediate in FT (0.43) and ET (0.40), and weakest in EPT (0.16) (p = 0.002). EPT patients could be distinguished by low coherence: coherence <0.18 in the wrist + elbow extensors differentiates EPT in this sample with a sensitivity of 86% and specificity of 84%. Results: Cumulant analysis showed predominantly alternating activity between wrist and elbow extensor in ET patients, while a more synchronous pattern was predominant in PD, EPT and FT (p = 0.008). EMG activity in wrist and elbow flexors tended to be more synchronous in PD (p = 0.059). Conclusion: Our results suggest that coherence and cumulant analysis may be of additional value in the diagnostic work-up of postural tremor. Significance: These additional measures may be helpful in diagnosing difficult tremor cases. (c) 2014 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.