Objective: Characterize the response of gait in a levodopa challenge test (LCT) in PD using inertial sensor-based 3D movement analysis and MDS-UPDRS.

Background: Quantitative 3D movement analysis using inertial measurement units (IMUs) allow a fine depiction of the sequence of motor response to a LCT. It is unknown how this measurement compares to that using MDS-UPDRS, the gold-standard to assess motor response in PD.

Method: 15 PD patients in selection for DBS were assessed in OFF state and every 20’ after a supra-threshold levodopa dose. At each time-point, patients walked 3x a 4-meter-long corridor. A full-body set of 15 IMUs was used to reconstruct patients’ gait 3D kinematics. MDS-UPDRS III items related to gait were used at each time-point. In OFF and Best ON, a full MDS-UPDRS III was performed

Results: Mean age and disease duration were 60.2±8.5 and 12.1±5.3 years, respectively. Total MDS-UPDRS III score was 47.9±8.6 (OFF) and 20.1±7.7 (Best On). In Best ON, gait speed, step length, stride length, cadence, swing time and single support significantly increased, while step time, stride time, double support, stance time, variability of step length and speed significantly decreased. At 20’ after levodopa, arm flexion and arm adduction range of motion, arm rotation and arm flexion angular velocity significantly increased. No significant changes were observed for step width, step length and step time asymmetry, swing time asymmetry, variability of stride time, stride length, step time, step width, double support or stance fraction. None of the items assessed by MDS-UPDRS III improved at 20‘. Principal Component Regression showed that kinematic features could explain ~50% of the MDS-UPDRS III variance. There was a significant and positive correlation between MDS-UPDRS III change (OFF vs BEST-ON) and gait speed, stride length, single support time, hip flexion, ankle angle, wrist deviation range of movement, hip adduction, hip rotation, ankle and elbow flexion angular velocity. Regularized discriminant analysis blindly classified patients based on IMUs features alone with an accuracy of 66.7±12.5% (OFF vs Best ON).

Conclusion: IMUs detect motor changes earlier than MDS-UPDRS and may be more sensitive for detection of changes induced by levodopa. Upper limbs improve earlier than lower limbs and gait with levodopa, possibly reflecting distinct thresholds of somatotopic regions in the striatum to dopamine

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MDS Abstracts - https://www.mdsabstracts.org/abstract/quantitative-3d-movement-analysis-detects-motor-improvement-earlier-than-mds-updrs-in-a-levodopa-challenge-test/