Validation of the MDS-UPDRS Part I for nonmotor symptoms in Parkinson's disease

The UPDRS has been the main outcome measure in studies of PD. Modifications have been made to improve scale properties and represent the breadth of manifestations of PD, particularly nonmotor symptoms (NMS), resulting in the Movement Disorder Society's revision of the UPDRS (MDS-UPDRS). This study was undertaken to determine the validity of MDS-UPDRS Part I (nonmotor experiences of daily living). The MDS-UPDRS and a number of validated scales for the NMS in PD were used in 94 patients with PD from Hoehn and Yahr stage I to V. We assessed reliability, floor and ceiling effects, and correlations with validated scales for the nonmotor symptoms of PD. MDS-UPDRS Part I showed high internal consistency (Cronbach's alpha: 0.85), small floor and ceiling effects (2% floor and 0% ceiling effect), and good concurrent validity (correlation with the original UPDRS Part I: r = 0.81, P < 0.001). The standardized z-score of the MDS-UPDRS Part I score demonstrated high convergent validity with the composite z-score of nonmotor scales (r = 0.89, P < 0.0001), and the two subscores based on the original factor analysis of Part I also had high correlations with the composite z-scores of corresponding nonmotor scales (depression, anxiety, apathy factor score: r = 0.72, P < 0.0001; other nonmotor features factor score: r = 0.87, P < 0.0001). Our data demonstrate that the MDS-UPDRS Part I total score has a strong relationship with a composite score of validated scales for the nonmotor aspects of PD.