Validation of a Patient-Reported Outcome Measure Sensitive to Diet and Nutraceutical Exposure in Parkinson’s Disease

Background: The Patient-Reported Outcomes in Parkinson’s Disease (PRO-PD) scale is a 35-item visual analog measure designed to quantify symptom severity across motor and non-motor domains. Developed as a continuous, patient-centered outcome, PRO-PD captures patient-perceived change over time and is suitable for remote longitudinal assessment. This study evaluated the psychometric properties of PRO-PD across two independent datasets, in-cluding reliability, validity, factor structure, and minimal clinically important change (MCIC), and assessed its relevance to nutrition- and lifestyle-focused research. Methods: Convergent validity was evaluated in a cross-sectional clinical dataset (n = 46) using established clinician-rated and patient-reported instruments, including Hoehn and Yahr, Unified Parkinson’s Disease Rating Scale (UPDRS), Parkinson’s Disease Questionnaire-39 (PDQ-39), Montreal Cognitive Assessment (MoCA), and PROMIS measures. Internal con-sistency, temporal stability, factor structure, and known-groups validity were assessed in a large remote-monitoring cohort (n = 2,612). MCID thresholds were estimated in a longitudinal sub-sample (n = 390) using anchor-based methods, multinomial regression, and receiver operating characteristic analyses. Joint modeling (two-stage procedure) approach was applied to model the sensitivity of PRO-PD change in time to the binary diet factors evolution in time. Results: PRO-PD demonstrated strong convergent validity with established clinical measures, excellent internal consistency (Cronbach’s α = 0.93–0.95), and good test–retest reliability (ICC = 0.78 overall; 0.89 at 6 months). Confirmatory testing of a previously proposed eight-factor structure showed suboptimal fit, leading to a parsimonious four-factor solution (Cognitive, Autonomic, Motor, Psycho-Emotional) explaining 47.6% of variance. PRO-PD scores increased significantly with advancing disease duration and stage. MCID thresholds were +53.5 points for worsening and −78.5 points for improvement (AUC = 0.63–0.71), with greater sensitivity for detecting deterioration than improvement. Joint modeling further demonstrated sensitivity of PRO-PD to baseline dietary behaviors and dietary change over time. Conclusions: These findings support PRO-PD as a psychometrically robust, low-burden out-come measure suitable for remote monitoring and for use across nutrition, nutraceutical, and pharmacologic intervention studies, including in early PD where traditional scales may lack sensitivity.