Objective: To analyze the construct validity of the Movement Disorders Society – Non Motor Rating Scale (MDS-NMS).

Background: The MDS-NMS is a new instrument that provides a comprehensive assessment of NMS in Parkinson’s disease (PD). Construct validity of the MDS-NMS, including convergent, discriminative and internal validity, has been assessed in order to determine its relationship with related constructs.

Method: Multi-center, cross-sectional study on MDS-NMS validation, with a sample of 402 PD patients recruited from clinics in UK and US. Information on socio-demographic characteristics and PD treatment was collected. The MDS-NMS (composed of 13 domains and a subscale on non-motor fluctuations, NMFs), Hoehn & Yahr staging (HY), MDS-Unified Parkinson’s disease Rating Scale (MDS-UPDRS), Non-Motor Symptoms Scale (NMSS), Clinical Impression of Severity Index for PD (CISI-PD), and Patient Global Impression of severity (PGI-S) were administered. For convergent validity, Spearman’s correlation coefficients of MDS-NMS with other variables were computed. Differences in MDS-NMS total score for the sample grouped by variables of interest were ascertained for discriminative validity. Internal validity was analyzed via the inter-correlation of MDS-NMS domains.

Results: The sample (62.2% men) had a mean age of 67.42 years old (standard deviation, SD: 9.96), PD duration of 8.2 years (SD: 5.93) and was mainly in HY stage 2 (54.5%). Mean scores were: MDS-NMS, 79.33 (SD: 65.87); NMFs, 6.87 (SD: 13.17). MDS-NMS total score correlated 0.26 with PD duration, 0.31 with levodopa-equivalent daily dose (LEDD), 0.53 with PGI-S, and 0.46 with CISI-PD. The NMFs subscale correlated 0.30 with PD duration, 0.42 with LEDD, 0.34 with PGI-S and 0.44 with CISI-PD. MDS-NMS domains showed correlation coefficients ranging 0.31-0.68 with corresponding MDS-UPDRS items and 0.39-0.87 with corresponding NMSS domains. NMFs correlated 0.72 with MDS-UPDRS fluctuations section. MDS-NMS total score showed no significant differences by sex and age, but it significantly increased with increasing HY stage, PD duration and LEDD (all p<0.001). NMFs scores were significantly different by HY stage (p=0.05). Correlations coefficients of MDS-NMS domains ranged from 0.05 to 0.70, with 41/78 of them being moderate.

Conclusion: The MDS-NMS is a clinically valid instrument to assess NMS in PD patients.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/construct-validity-of-the-movement-disorders-society-non-motor-rating-scale-mds-nms/