Conversion between NMSS and MDS-NMS in Parkinson's Disease

Background: The burden of non-motor symptoms in Parkinson's disease (PD) can be measured with the Non-Motor Symptoms Scale (NMSS) and the International Parkinson and Movement Disorder Society Non-Motor Rating Scale (MDS-NMS), for which scoring systems, structure and clinical coverage differ. Objectives: The goal was to develop conversion formulas between the NMSS and the MDS-NMS scores. Methods: Data from 402 patients with PD participating in the primary MDS-NMS validation study were used. The association between domain and total scores of both scales was assessed by the Spearman rank correlation coefficient and Kendall's W concordance coefficient. Equations for between-scale transformation of total score were constructed from weighted linear regression models. Results: Spearman rank correlations showed that MDS-NMS domains correlated 0.39 to 0.88 with the corresponding NMSS domains. The equation for transforming the NMSS total score to MDS-NMS total score is: MDS-NMS = 11.629 + 1.624 x NMSS (P < 0.001, R-2 = 0.748). For converting the MDS-NMS total score to NMSS total score, the formula is NMSS = 2.475 + 0.495 x MDS-NMS (P < 0.001, R-2 = 0.771). Conclusions: Our conversion equations enable direct comparison of the NMSS and MDS-NMS instruments, facilitating data comparability across studies. (c) 2025 International Parkinson and Movement Disorder Society.