Determinants of objectively measured physical functional performance in early to mid-stage Parkinson disease

Background: Parkinson disease (PD) may lead to functional limitations through both motor and nonmotor symptoms. Although patients with advanced disease have well-documented and profound functional limitations, less is known about the determinants of function in early to mid-stage disease where interventions may be more likely to benefit and preserve function.

Objective: The objective of the current study was to identify motor, cognitive, and gait determinants of physical functional performance in patients with early to mid-stage PD.

Design: This was a secondary analysis of cross-sectional baseline data from a randomized clinical trial of exercise.

Setting: The study was performed at a tertiary academic medical center.

Participants: The study included 121 patients with early to mid-stage PD.

Methods: Our functional performance outcomes included the following: the Continuous Scale Physical Functional Performance Test (CS-PFP; primary outcome); the Timed Up and Go test (TUG); and Section 2 (Activities of Daily Living) of the Unified Parkinson's Disease Rating Scale (UPDRS). Explanatory variables included measures of disease severity, motor function, cognitive function, balance, and gait. Stepwise linear regression models were used to determine correlations between explanatory variables and outcome measures.

Results: In our regression models, the CS-PFP significantly correlated with walking endurance (Six-Minute Walk Test; r(2) = 0.12, P < .0001), turning ability (360° Turn Test; r(2) = 0.03, P = .002), attention (Brief Test of Attention; r(2) = 0.01, P = .03), overall cognitive status (Mini-Mental State Examination; r(2) = 0.01, P = .04), and bradykinesia (timed tapping; r(2) = 0.02, P = .02). The TUG significantly correlated with walking speed (5-Meter Walk Test; r(2) = 0.33, P < .0001), stride length (r(2) = 0.25, P < .0001), turning ability (360° turn, r(2) = 0.05, P = .0003), and attention (r(2) = 0.016, P = .03). Section 2 of the UPDRS was significantly correlated with endurance (r(2) = 0.09, P < .0001), turning ability (r(2) = 0.03, P = .001), and attention (r(2) = 0.01, P = .03).

Conclusions: Gait, motor, and cognitive function all contribute to objectively measured global functional ability in mild to moderate PD. Subjectively measured functional activity outcomes may underestimate the impact of both motor and nonmotor symptoms.