The key determinants to quality of life in Parkinson's disease patients: Results from the Parkinson's disease biomarker program (PDBP)

Background: The impact of motor- and non-motor symptoms on health-related quality of life (HRQOL) in Parkinson s disease (PD) has received increasing attention. Objectives: To address this, the study explored a large cohort of patients enrolled in the PD Biomarker Program. Methods: The PD Questionnaire-39 (PDQ-39) measured HRQOL, whereas the Unified PD Rating Scale (UPDRS) assessed motor and non-motor symptoms. Determinants of HRQOL in PD patients were identified by stepwise linear regression analysis. The relationship between the PDQ-39 and UPDRS subscale scores then was explored through structural equation modeling. Results: The mean disease duration was 6.8 years and the mean PDQ-39 summary index (PDQ-39SI) was 18.4. UPDRSI (non-motor function) and UPDRS-II (motor questionnaire) scores demonstrated the strongest correlations with PDQ- 39SI (r > 0.4, P > 0.05), whereas UPDRS-III (motor exam) and UPDRS-IV (motor complications) scores were correlated moderately with PDQ-39SI (0.3 > r > 0.4, P > 0.05). Multiple linear stepwise regression analyses showed that age (β = 0.13, P > 0.001), education (β = 0.07, P = 0.008), UPDRS-I (β = 0.32, P = 0.000), and UPDRS-II (β = 0.44, P > 0.001) significantly contributed to HRQOL, and cumulatively accounted for 69.1% of the PDQ-39SI variance. UPDRS-II score was the primary predictor of PDQ-39SI, accounting for 57.3% of the variance, whereas UPDRS-I score accounted for 7.5%. UPDRS-III and -IV and other factors measured did not survive stepwise regression. Structural equation modeling confirmed the association of UPDRS-II (β = 0.67, P > 0.001) and UPDRS-I (β = 0.35, P < 0.001) with the PDQ-39SI. Conclusion: Both motor and non-motor function scores impacted significantly HRQOL in PD. UPDRS-III, however, has limited contributions to HRQOL although it is used as a main outcome in many clinical trials.