Objective: This study aims to validate the two-domain structure of MDS-UPDRS Part III items in both medication states, exploring the discriminative ability of the tremor and nontremor items in capturing the severity of PD symptoms in patients undergoing treatment changes.

Background: The Movement Disorder Society Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) Part III is a critical tool for evaluating motor symptoms in Parkinson’s disease (PD), comprising a detailed examination of 33 items. Prior analyses have identified two distinct domains within this part: tremor and nontremor, which exhibit varying responses to PD medication states (ON and OFF). Understanding these variations is essential for precise symptom assessment.

Method: We analyzed MDS-UPDRS data from 7,963 PD patients (6,218 ON and 1,745 OFF medication) using Item Response Theory (IRT) modeling to estimate discrimination parameters for the tremor (10 items) and nontremor (23 items) domains separately. Discrimination values were categorized from “none” to “very high” to assess item effectiveness in determining overall PD severity in both ON and OFF states.

Results: The IRT analysis revealed high to very high discrimination parameters across all Part III items for both states, with mean discrimination values of 1.963 (ON state) and 2.125 (OFF state). This indicates a robust capacity of Part III items to distinguish between different severity levels of parkinsonian symptoms under varying medication effects. Notably, discrimination scores were generally higher in the OFF state, aligning with expectations for a disability/impairment measure.

Conclusion: Our findings affirm the structural integrity and discriminative power of the MDS-UPDRS Part III’s two-domain model in both ON and OFF medication states. This consistency across states underscores the tool’s utility for longitudinal studies, motor fluctuation assessments, and clinical trials involving PD patients. Future studies may further explore these domains in relation to patient outcomes and treatment efficacy.

References: Guo Y, Stebbins GT, Mestre TA, Goetz CG, Luo S. Movement Disorder Society Unified Parkinson’s Disease Rating Scale Motor Examination Retains Its 2‐Domain Profile in Both On and Off States. Movement Disorders Clinical Practice. 2022 Nov;9(8):1149.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/movement-disorder-society-unified-parkinsons-disease-rating-scale-motor-examination-retains-its-2-domain-profile-in-both-on-and-off-states/