Objective: we hypothesize that the complexity of the hand tremor would be sensitive to and identifiable between those the PT and ET.

Background: Tremor is a common movement disorder, which is often observed in two pathological conditions: parkinsonian tremor (PT) and essential tremor (ET). The PT and ET are often misdiagnosed in clinics. The spontaneous motion of tremor is dependent upon numerous physiological interactions over multiple temporal-spatial scales. The dynamics of the tremor is thus “complex”, containing meaningful information pertaining to the underlying physiological function. However, the characteristics of such physiologic complexity in PT and ET still remain unknown.

Method: Forty-eight participants with clinically-diagnosed PT and 48 age-matched participants with ET completed this study. With the wearable accelerometers attached on hand, participants completed two 30-second tests to measure the ampliude of tremor in both left and right hand within each of following conditions: sitting while arms were at resting state (i.e., resting tremor) and while arms were outstretched horizontally (i.e., postural tremor). The multiscale entropy (MSE) was then used to quantify the complexity of the amplitude time series. Greater MSE means greater complexity.

Results: Participants with ET had significantly lower complexity of both resting and postural tremor in left and right hands compared to those with PT (F>9.7, p<0.002), even after adjusted for age and the status “if obvious tremor was presented during tests”. Those with lower complexity of hand tremor had longer course of diseases (PT: r2>0.19, p<0.009; ET: r2>0.18, p<0.005). Within the PT group, those with lower complexity had greater UPDRS-III scores (r2>0.20, p<0.006). Moreover, the Receiver operating characteristic (ROC) curve demonstrated that using the average postural tremor complexity of left and right hand can identify the PT and ET (AUC=0.88, cut-off value=48).

Conclusion: We here demonstrate first-of-its-kind evidence that the physiological complexity of hand tremor captures different pathology in PT and ET, and is sensitive to the disease duration and severity. More importantly, the ROC analysis revealed that this complexity metric may serve as a novel marker to help the identification of these pathological conditions in clinical practice.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-physiologic-complexity-of-hand-tremor-identifies-parkinsonian-tremor-and-essential-tremor/