Analyzing 180 degrees turns using an inertial system reveals early signs of progression of Parkinson's disease.

Changes in turning are one of the early motor deficiencies in Parkinson's Disease (PD). We have proposed a system based on wearable, inertial sensors and a novel automatic analysis algorithm that can assess 180 degrees turns. Twelve patients in early stages of PD and 14 age-matched healthy subjects were enrolled in this study. Inertial sensors were attached on shanks and sternum. Measurement protocol included walking on a straight pathway, turning 180 degrees and returning back. Subjects were measured 4 times, once every 6 months during an 18 months period. At the baseline, 9 subjects from each group repeated the test twice to assess test-retest reliability. Patients with mild PD had a very low Postural Instability Gait Difficulty (PIGD subscore of UPDRS III) score (average 0.67, min 0, max 3). The analysis showed that the patients had a significantly longer turning duration (2.18+/-0.43 vs. 1.79+/-0.27 seconds, p<0.02) and longer delay in their last step before initiating a turn (0.56+/-0.04 vs. 0.52+/-0.04 seconds, p<0.03). Estimated turning duration and other metrics had a high test-retest reliability (rho>0.85). Turning duration also showed a significant Group *Time interaction (p<0.03) during the longitudinal study highlighting early signs of the progression of the disease.