Evaluation of severity of predominantly non-dopaminergic symptoms in Parkinson's disease: The SENS-PD scale.

INTRODUCTION In spite of the multisystem nature of Parkinson's disease (PD), the formal assessment of its impairments is focused on symptoms predominantly reflecting degeneration of dopaminergic neurons. The aim of this study was to develop a valid and reliable rating scale of predominantly non-dopaminergic (PND) symptoms, which can be used as an additional measure of severity and progression of PD. METHODS Using data of the PROPARK (N = 396) and ELEP (N = 365) cohorts, three items were selected from each of six selected PND domains (cognitive impairment, depressive symptoms, excessive daytime sleepiness, psychotic symptoms, autonomic dysfunction and Postural-Instability-and-Gait-Difficulty), based on item-total correlations. Hereafter, we evaluated reliability and validity of the resulting scale. RESULTS The 18-item PND scale showed to be reliable and valid. Cronbach's alpha was 0.83. Principal component analysis using the six domain scores resulted in one factor, justifying the calculation of a sum score. Correlation coefficients of the sum score with severity of non-motor symptoms (non-motor part of MDS-UPDRS), motor symptoms (SPES/SCOPA scale), and Hoehn and Yahr stage were 0.63, 0.41 and 0.48, respectively (p < 0.001). CONCLUSION We developed a short, reliable and valid scale to evaluate severity of PND symptoms in PD. The score is expected to be largely insensitive to dopaminergic effects and may therefore more accurately reflect severity and progression of the underlying disease than currently used dopamine-sensitive measures. In combination with assessment of predominantly dopaminergic (motor) symptoms, a broad yet concise evaluation of PD is obtained, which better captures the widespread clinical consequences of the multisystem disease.