Validation of the Norwegian version of the Movement Disorder Society-Unified Parkinson’s Disease Rating Scale

Introduction: The Movement Disorder Society-revised version of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS) is the gold standard assessment for evaluating Parkinson's disease (PD) symptoms and severity, but a validated Norwegian version is not yet available. We translated the original English MDS-UPDRS into Norwegian and tested the clinimetrics of the translated version following the MDS-established protocol for non-English language translations. Methods: Two independent teams translated the English version of the MDS-UPDRS into Norwegian. After review of the back-translated English version, cognitive pretesting was performed in twelve PD patients at one study site. This was followed by large-scale testing completed by 351 native Norwegian-speaking PD patients at six centers across Norway. We applied confirmatory and exploratory factor analyses to determine the validity of the Norwegian version. Additional analyses were performed to test the reliability of the translated scale. Results: Confirmatory factor analysis demonstrated that the factor structure of the Norwegian version was consistent with that of the English version, as indicated by comparative fit indexes of ≥0.90 for all four MDS-UPDRS parts. Exploratory factor analysis showed the same number of factors in each MDS-UPDRS part, compared to the English version, with some differences in item loadings. Cronbach's α values were >0.70 for all four MDS-UPDRS parts. Conclusion: The Norwegian language MDS-UPDRS has good construct validity and internal consistency, meeting the requirements to be designated as the Official Norwegian Version of the MDS-UPDRS. We recommend using this validated version in both research and clinical practice.