Intraoperative Quantification of MDS-UPDRS Tremor Measurements Using 3D Accelerometry: A Pilot Study

Abstract

The most frequently used method for evaluating tremor in Parkinson’s disease (PD) is currently the internationally standardized Movement Disorder Society—Unified PD Rating Scale (MDS-UPDRS). However, the MDS-UPDRS is associated with limitations, such as its inherent subjectivity and reliance on experienced raters. Objective motor measurements using accelerometry may overcome the shortcomings of visually scored scales. Therefore, the current study focuses on translating the MDS-UPDRS tremor tests into an objective scoring method using 3D accelerometry. An algorithm to measure and classify tremor according to MDS-UPDRS criteria is proposed. For this study, 28 PD patients undergoing neurosurgical treatment and 26 healthy control subjects were included. Both groups underwent MDS-UPDRS tests to rate tremor severity, while accelerometric measurements were performed at the index fingers. All measurements were performed in an off-medication state. Quantitative measures were calculated from the 3D acceleration data, such as tremor amplitude and area-under-the-curve of power in the 4–6 Hz range. Agreement between MDS-UPDRS tremor scores and objective accelerometric scores was investigated. The trends were consistent with the logarithmic relationship between tremor amplitude and MDS-UPDRS score reported in previous studies. The accelerometric scores showed a substantial concordance (>69.6%) with the MDS-UPDRS ratings. However, accelerometric kinetic tremor measures poorly associated with the given MDS-UPDRS scores (R2 < 0.3), mainly due to the noise between 4 and 6 Hz found in the healthy controls. This study shows that MDS-UDPRS tremor tests can be translated to objective accelerometric measurements. However, discrepancies were found between accelerometric kinetic tremor measures and MDS-UDPRS ratings. This technology has the potential to reduce rater dependency of MDS-UPDRS measurements and allow more objective intraoperative monitoring of tremor.

Supine MDS-UPDRS-III Assessment: An Explorative Study

“…Two wired tri-axial accelerometers (MMA8452Q tri-Axis, Freescale Semiconductor, Inc., Austin, TX, USA) with a ±2 g range and a 200 Hz sampling rate were used, as previously described by Smid et al [3]. Accelerometry data were recorded with LabVIEW v. 2014 (National Instruments, Austin, TX, USA).…”

“…During surgery, MDS-UPDRS-III testing is performed in the supine position, since patients are situated on the operating table with the head fixated in a stereotactic frame. Several studies have used the MDS-UPDRS-III in the supine position [2][3][4][5][6], even though the MDS-UPDRS-III was originally validated in the sitting position [7]. Therefore, the primary aim of this prospective study is to investigate the agreement between MDS-UPDRS-III assessments in sitting and supine position, in order to endorse the supine application of the MDS-UPDRS-III.…”

“…All tasks were recorded on video. Accelerometry data (with sensors on both index fingers) were recorded for upper extremity tremor (items 15 and 17), as described previously [3].…”

“…Signal analysis was performed in MATLAB v. 2021a (MathWorks, Natick, MA, USA). Pre-processing of tri-axial acceleration data was performed as described by Smid et al [3]. Accelerometric data measured during the upper extremity tremor tasks (items 15 and 17) were used to assess postural and rest tremor amplitude.…”

“…Contrast coding of MDS-UDPRS-III tremor scores was defined to be orthogonal polynomial, of which the first contrast coefficient has a linear trend, to assess linearity between MDS-UPDRS tremor scores and the logarithm (log10) of the accelerometric tremor amplitude [3,12], assessed separately in sitting and supine positions. MDS-UPDRS tremor scores of the two raters were averaged and rounded per measurement.…”