Identifying axial and cognitive correlates in patients with Parkinson's disease motor subtype using the instrumented Timed Up and Go

Parkinson's disease (PD) is clinically highly heterogeneous, often divided into tremor dominant (TD) and postural instability gait difficulty (PIGD). To better understand these subtypes and to help stratify patients, we applied an objective marker, i.e., an instrumented version of the traditional "Timed Up and Go" test (iTUG). It is not known whether the iTUG is sensitive to PD motor phenotypes or what are its behavioral and cognitive correlates. Subjects performed the iTUG wearing a body-fixed sensor. Subcomponents were studied including walking, transitions and turning. Gait, balance and cognitive function and the associations between iTUG, behavioral and cognitive domains were assessed. We also compared two representative subtypes, with minimal symptom overlap, referred to here as predominant PIGD (p-PIGD) and predominant TD (p-TD). One hundred and six patients with PD performed the iTUG. Significant correlations were found between iTUG measures and the PIGD score, but not with TD score. Thirty p-PIGD and 31 p-TD patients were identified. Both groups were similar with respect to age and disease duration (p > 0.75). The p-PIGD patients took significantly longer to complete the iTUG (p = 0.026), used more steps (p = 0.031), albeit with similar step duration (p = 0.936). In the sit-to-stand transition, the p-PIGD patients exhibited lower anterior-posterior jerk (p = 0.04) and lower pitch range (p = 0.012). During the turn, the p-PIGD patients had a lower yaw amplitude (p < 0.038). Cognitive domains were correlated with iTUG measures in the p-PIGD patients, but not in the p-TD. These findings demonstrate that a single sensor can identify axial and cognitive correlates using subcomponents of the iTUG and reveals subtle alterations between the PD motor subtypes.