The impact of non-motor symptoms on health-related quality of life of patients with Parkinson's disease

Background: Non-motor symptoms are detrimental to health-related quality of life (HRQoL) of Parkinson's disease patients. In this study, the Non-Motor Symptoms Scale (NMSS) was used to assess the impact of the non-motor symptoms on HRQoL of Parkinson's disease patients. Methods: In a multicenter, international, cross sectional study on 411 Parkinson's disease patients, the NMSS was applied along with clinical (Hoehn and Yahr staging and SCOPA-Motor) and HRQoL measures (PDQ-39, and EQ5D). Prevalence of non-motor symptoms was determined also through the NMSS. The association of NMSS and SCOPA-Motor with HRQoL measures and the differences in HRQoL scores between patients with and without nonmotor symptoms in each NMSS domain were estimated by non-parametric statistics. Predictors of HRQoL were sought through multiple linear regression analyses. Results: Nocturia (68.4% of the sample), fatigue (65.9%), and dribbling saliva (56.7%), were the most frequent complaints. Total NMSS score: (1) showed a higher correlation coefficient (r(S) = 0.70) with the PDQ-39 Summary Index (1) than SCOPA-Motor (r(S) = 0.58); (2) showed high-moderate correlation (r(S) = 0.60 - 0.38) with all PDQ-39 domains; and (3) was the best predictor of HRQoL as measured by the PDQ-39 SI. For each NMSS domain, patients with symptoms had significantly worse HRQoL scores than patients without symptoms. Discussion: To our knowledge, this is the first study to determine in a holistic manner the impact of the non-motor symptoms on HRQoL of Parkinson's disease patients. The results show that non-motor symptoms have, as a whole, a greater impact on HRQoL than motor symptoms and non-motor symptoms progression contributes importantly to HRQoL decline in patients with Parkinson's disease