Abstract
A considerable number of patients presenting with tremor are misdiagnosed resulting in suboptimal treatment and incorrect prognosis. The clinical di↵erential diagnosis of tremor syndromes is challenging and, unfortunately, there is a lack of accurate diagnostic tools that can reliably distinguish between even the most common tremor aetiologies, i. e. Parkinsonian tremor and essential tremor (ET). We introduce a tremor evaluation protocol exploiting specific activating conditions, ‘hands completely prone/stretched’ (action tremor) for ET and ‘hands hanging down’ (rest tremor) for Parkinsonian tremor, in conjunction with novel miniature inertial measurement units (IMUs), which allow for a non-invasive and accurate analysis of tremor. A total of 14 patients with ET and 14 patients with Parkinson’s disease (PD) were recruited from our outpatient movement disorders clinic at the University Hospital Zurich. The total acceleration from the three pairwise-perpendicular accelerometric axes during the 1 minute blocks of the two handpositions were computed and high-passed filtered at 2 Hz. The power spectral density during each block was calculated and summed up over the frequency domain. Tremor increased significantly in PD patients when transitioning from the action to the rest tremor position (Wilcoxon signed rank test, p = 0.0068). Contrarily, tremor increased in 75 % of ET patients during the transition from the rest to the action tremor hands position. Moreover, tremor was significantly higher in PD as compared to ET during the rest tremor hands position (Wilcoxon rank sum test, p = 0.0262). 77 % of patients showing an increase in tremor amplitude from the action to the rest tremor hands position position had PD, while 82 % of patients showing a decrease of the tremor amplitude during the same transition had ET. 1 The findings of this study support an inverse tremor activation pattern for patients with PD vs. ET when transitioning between the rest and action tremor hands position that can be detected by IMUs, thereby assisting in guiding the di↵erential diagnosis. Besides, IMUs are non-invasive, non-obtrusive, light, cheap and could be widely distributed. Thus, this study motivates the incorporation of this promising tool and short clinical assessment protocol into the routine clinical evaluation of patients presenting with tremor. Special focus should be on the tremor pattern during the transition from the rest to the action tremor hands position as well as the tremor amplitude during the rest tremor hands position.
Bichsel, Oliver