Objective: To determine whether subsets of MDS-UPDRS Part III items have equal or better prognostic value than the full scale for initiation of dopaminergic therapy in early Parkinson’s disease (PD).

Background: The MDS-UPDRS Part III is the standard clinician-rated PD motor impairment assessment, yet the prognostic value of its individual items or item subsets remains unclear. Whereas reduced subsets from patient-reported Parts IB and II preserve, even amplify, prognostic utility, the validity of a similar Part III reduction is unknown.

Method: Harmonized longitudinal data from six early PD cohorts measuring time to the initiation of dopaminergic treatment as the primary outcome, were analyzed using longitudinal item response theory models to rank items by their discrimination and information functions. Ranked items were assembled into cumulative subsets, and time to dopaminergic therapy initiation was evaluated using time-varying Cox models under full, 1-year, and 2-year follow-up windows. Subset performance was compared with full-item models using concordance indices and likelihood ratio tests, with successful subsets defined by stability and superior performance across analytic windows.

Results: We did not identify a subset of items meeting the predefined criteria for predictive stability or superiority over the full Part III scale. Non-tremor motor items showed stronger longitudinal sensitivity and prognostic utility, however, when compared with tremor items (C-index: 0.591-0.605 vs 0.554-0.562).

Conclusion: Unlike patient-reported Parts IB and II, MDS-UPDRS Part III cannot be reliably reduced for prognostic modeling in early PD for time to dopaminergic use. The full MDS-UPDRS Part III remains necessary for accurate outcome prediction.

References: Alam MS, Yu L, Stebbins GT, Mestre TA, Goetz CG, Luo S. Longitudinal Evaluation of an Abbreviated Patient-Reported Movement Disorder Society-sponsored revision of the Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) for Predicting Dopaminergic Therapy Initiation in Early Parkinson’s Disease. Mov Disord 2025;OnlineFirst.

Zou H, Goetz CG, Stebbins GT, Mestre TA, Luo S. Increasing Sensitivity in Patient-Reported MDS-UPDRS Items for Predicting Medication Initiation in Early PD. Mov Disord Clin Pract 2025;12:148–156.

Luo S, Zou H, Goetz CG, et al. Novel Approach to Movement Disorder Society-Unified Parkinson’s Disease Rating Scale Monitoring in Clinical Trials: Longitudinal Item Response Theory Models. Mov Disord Clin Pract 2021;8:1083–1091.

Luo S, Zou H, Stebbins GT, et al. Dissecting the Domains of Parkinson’s Disease: Insights from Longitudinal Item Response Theory Modeling. Mov Disord 2022;37:1904–1914.

Guo Y, Goetz CG, Stebbins GT, Mestre TA, Luo S. Using Movement Disorder Society Unified Parkinson’s Disease Rating Scale Parts 2 and 3 Simultaneously: Combining the Patient Voice with Clinician Ratings. Mov Disord 2023;38:453–463.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/mds-updrs-part-iii-cannot-be-reliably-reduced-for-prognostic-modeling-in-early-parkinsons-disease/