Abstract
Due to a lack of reliable non-invasive bio-markers, misdiagnosis between Parkinson's disease and essential tremor is common. Although some assistive engineering approaches have been proposed, little acceptance has been obtained for these methods lack well-studied mechanisms and involve operator-dependent procedures. Aiming at a better differentiation between the two tremor causes, we present a novel posture, termed arm-rested posture, to ameliorate the quality of recorded tremor sequences. To investigate its efficacy, the posture was compared with another common posture, called arm-stretching posture, in fundamental aspects of tremor intensity and dominant frequency. A tremor-affected cohort comprising 50 subjects (PD = 26, ET = 24) with inhomogeneous tremor manifestation were recruited. From each subject, acceleration data of 5 min in terms of each posture were recorded. In the overall process, no operator-dependent procedures, such as data screening, was employed. The differentiation performance of the two postures were assessed by the index of discrimination coefficient and a receiver operating characteristic analysis based on binary logistic regression. The results of the differentiation assessment consistently demonstrate a better performance with the arm-rested posture than with the arm-stretching posture. As a by-product, factors of disease stage (incipient, progressed stage), spectrum estimate (PSD, bispectrum) and recording length (5–300s) were investigated. The significant effect of disease stage was only found in PD in terms of tremor intensity [F(1, 516) = 7.781, P < 0.05]. The bispectrum estimate was found to have better performance than the PSD estimate in extracting dominant frequency in terms of the discrimination coefficient. By extending the recording length, we noticed an increase in the performance of dominant frequency. The best result of the arm-rested posture was obtained with the maximum recording length of 300 s (area under the curve: 0.944, sensitivity: 92%, 1-specificity: 0%, accuracy: 96%), which is better than that of the arm-stretching posture in the same condition (area under the curve: 0.734, sensitivity: 54%, 1-specificity: 12%, accuracy: 72%). Thus, we conclude that the arm-rested posture can assist in improving tremor differentiation between Parkinson's disease and essential tremor and may act as a universal tool to analyze tremor for both clinical and research purpose.
Highlights
Different from physiological tremor that accompanies normal body movements (Raethjen et al, 2000), pathological tremor impairs the flexibility and coordination of motor function by eliciting large-amplitude involuntary muscle oscillation activities (Rocon et al, 2004; Helmich et al, 2013)
Simple effect analysis with independent-sample t-tests showed a significant difference between the Parkinson’s disease (PD) cohort and the essential tremor (ET) cohort with the arm-rested posture (P2) [t(498) = 14.633, P < 0.05], while there was no significant difference between the PD cohort and the ET cohort with the arm-stretching posture (P1) [t(498) = −1.813, P = 0.069]
Further results of simple effect analysis showed there was a significant difference between the incipient stage (S1) and the progressed stage (S2) of PD with the arm-stretched posture (P1) [t(258) = −5.226, P < 0.05] and no significant difference between the two stages of PD with the arm-rested posture (P2) [t(258) = −0.267, P = 0.790]
Summary
Different from physiological tremor that accompanies normal body movements (Raethjen et al, 2000), pathological tremor impairs the flexibility and coordination of motor function by eliciting large-amplitude involuntary muscle oscillation activities (Rocon et al, 2004; Helmich et al, 2013). Among its 11 confirmed etiologies (Deuschl et al, 1998), Parkinson’s disease (PD) and essential tremor (ET) account for up to 90% of the tremoraffected population (Deuschl et al, 1998; Thanvi et al, 2006). Even between these two most common causes, there is a high rate of misdiagnosis. 25% of the PD patients are misdiagnosed as ET cases (Rizzo et al, 2016). The optimal medical treatment of these PD patients is delayed. The best opportunity of controlling the irreversible progress of the disease is missed (Mark, 2007)
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