Independent validation of Parkinson’s disease Sleep Scale 2nd version (PDSS-2)

Sleep problems are one of the most common non-motor symptoms of Parkinson’s disease (PD). The Parkinson’s disease Sleep Scale 2nd version (PDSS-2) was published in 2011 showing satisfactory clinimetric results. We performed an independent testing of the scale adding further information on its clinimetric properties. In this nationwide study 537 PD patients were enrolled. Besides PDSS-2, we assessed Patient’s Global Impression-Severity (PGI) scale on sleep disturbances, Non-motor Symptoms Scale and MDS-UPDRS. Following the Classical Theory of Tests we performed descriptive data analysis, factor analysis, reliability, validity and precision measurements. Subsequently, we evaluated cut-off value for detecting clinically meaningful sleep problems based on receiver operating characteristics analysis. Based on the PGI scale, 161 patients (30.0 %) did not reported any sleep problems. Factor analysis revealed almost the same factor structure described by the original PDSS-2 validation study. Cronbach’s alpha was 0.863 and all item had good item-total correlation. PDSS-2 demonstrated high convergent validity with Non-Motor Symptoms Scale and Clinical Global Impression-Severity and non-motor part of MDS-UPDRS, and divergent validity with age, gender, education level, disease-duration and Hoehn–Yahr Stages. Presence of sleep problems was identified by scores >10.5 points on PDSS-2 (sensitivity 85.3 %, specificity 60.8 %, diagnostic accuracy 78.1 %); whereas scores >19.5 points indicated marked sleep-related problems (specificity 68.5 %, sensitivity 78.0 %, diagnostic accuracy 74.3 %). Independent and cross-cultural validation of patient reported outcomes is essential to confirm or reject the findings obtained by the developers of the scale. Our results demonstrate that fundamental clinimetric properties of the PDSS-2 are satisfactory.