Clinical Correlates of a Ratio‐Based Progression Index in Parkinson's Disease: Insights from a Large Cross‐Sectional Cohort

Background Assessment of disease progression in Parkinson's disease (PD) usually relies on longitudinal follow‐up, which is often impractical in large real‐world cohorts. Cross‐sectional approaches may provide pragmatic proxies to explore relative motor deterioration using routine clinical data. Objectives To explore clinical and non‐motor correlates of estimated relative motor progression in PD using a simple ratio‐based index—MDS‐UPDRS Part III (OFF medication) divided by disease duration. Methods In this retrospective cross‐sectional study, 711 patients with idiopathic PD were classified as slow or fast progressors based on the cohort median of the MDS‐UPDRS III (OFF)/disease duration ratio (7.31 points/year). Motor, non‐motor, demographic, and treatment‐related variables were compared between groups. Multivariable logistic regression analyses were used to identify clinical features associated with higher estimated progression. Results Patients with higher estimated motor burden per year showed greater non‐motor symptom burden, higher residual motor load (ON/OFF ratio), and a higher prevalence of the akinetic‐rigid phenotype. In multivariable analyses, non‐motor symptom burden, residual motor ratio, shorter disease duration, and akinetic‐rigid phenotype were independently associated with higher estimated progression. Among non‐motor domains, Sleep/Fatigue and Miscellaneous symptoms showed specific associations. The models demonstrated good within‐cohort explanatory performance (Nagelkerke R 2 = 0.42–0.47) in this cross‐sectional cohort. Conclusions This study presents a simple ratio‐based proxy to explore relative motor progression in PD. While not a validated longitudinal progression measure, it may serve as a pragmatic exploratory tool for descriptive stratification of large clinical cohorts. Longitudinal validation is required.