Objective: To quantify tremor characteristics using inertial sensors in functional and organic tremor patients and to present the differences in tremor quantification between these two groups, during long term tremor recordings and to determine the minimum number of days necessary to obtain reliable estimates.

Background: Distinguishing tremor types is important for treatment and prognosis. One major distinction is between tremor with an organic cause (organic tremor; OT) and functional tremor (FT). FT tends to have less stable characteristics compared to organic tremor; exhibiting frequent interruptions, irregularities and frequency changes [1]. Fluctuations in tremor characteristics affect all patients, making it difficult to assess these from a momentary observation in the clinic. Long-term continuous monitoring would facilitate overall occurrence and treatment response assessment.

Methods: Inertial sensor data were recorded from 44 tremor patients (16 FT, 28 OT) during unconstrained activities of daily living during 30 days, each day over a 10-hour period. Sensors were attached to the dorsal side of the forearm (close to the wrist). Start and end of recording per day were obtained from electronic patient diaries. The accelerometer signal and a tremor identification algorithm [2] implementing the periodogram were used to identify time windows with tremor, from which the percentage of tremor and tremor frequency variability were calculated per patient across all days. Non-parametric distributions were generated and Z-tests performed to determine whether estimates of tremor characteristics obtained from the first 3, 5, 7 or 10 days were representative of estimates obtained from any 3, 5, 7 or 10 days within the 30 days.

Results: Tremor percentage ranged from 10 to 34% for FT patients and from 4.7 to 70.0% for OT patients. Frequency variability ranged from 0.6 to 2.1 Hz for FT patients and from 0.4 to 1.5 Hz for OT patients. Seven days of tremor recording were the minimum number of days resulting in a non-significant Z-test, meaning that seven days are the shortest period of time needed to obtain reliable estimates of tremor characteristics.

Conclusions: Using long-term recordings with inertial sensors, fluctuations in tremor characteristics over the days could be observed in FT as well as OT patients based on percentage of tremor and tremor frequency variability. Seven days of recording are sufficient to determine these characteristics reliably.

References: [1] P. E. O’Suilleabhain and J. Y. Matsumoto, “Time-frequency analysis of tremors.,” Brain, vol. 121 ( Pt 11), pp. 2127–34, Nov. 1998. [2] O. Martinez Manzanera, J. W. Elting, J. H. van der Hoeven, and N. M. Maurits, “Tremor Detection Using Parametric and Non-Parametric Spectral Estimation Methods: A Comparison with Clinical Assessment,” PLoS One, vol. 11, no. 6, p. e0156822, Jun. 2016.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/quantitative-characterisation-of-tremor-in-functional-and-organic-tremor-patients/