The Influence of Motor and Nonmotor Factors on Ambulatory Activity in People With Parkinson Disease

BACKGROUND AND PURPOSE: Reduction in ambulation levels has been described as a clinical "red flag" that represents the emergence of disability in individuals with Parkinson disease (PD). Multiday ambulatory activity measures may capture disability not detected by standard clinical assessments. However, the influence of disease severity and nonmotor symptoms on ambulatory activity remains unclear. This study aimed to examine the association between daily ambulatory activity and motor disease severity, assessed in both medication states, and to identify which non-motor symptoms were associated with daily step accumulation in individuals with mild to moderate PD. METHODS: Mean daily steps were calculated over 7 days in 198 participants with PD. Motor and nonmotor symptoms were characterized using Movement Disorders Society-Unified Parkinson Disease Rating Scale (MDS-UPDRS) Part I, III, and IV. Descriptive statistics were calculated at baseline to characterize participant demographics and clinical characteristics. Linear regressions modeled the association between motor/nonmotor signs/symptoms and ambulatory activity, adjusting for age, race, and body mass index. RESULTS: Median daily step count was 5180 (interquartile range: 3521-7199). Standardized off-medication MDS-UPDRS III scores were significantly associated with fewer mean daily steps, while on-medication scores were not, though the magnitude of this association was modest. Among nonmotor symptoms, a self-reported complaint of lightheadedness upon standing was associated with approximately 2000 fewer mean daily steps. CONCLUSION: A self-report of lightheadedness upon standing showed a clinically meaningful association with reduced ambulatory activity, while motor severity, even assessed in the standardized off-medication state, showed only a modest association. These findings highlight the value of nonmotor symptom assessment, particularly cardiovascular autonomic screening, in understanding real-world disability in PD.