Association between the prognostic nutritional index and impulse control disorders in patients with early-stage Parkinson's disease
Background Impulse control disorders (ICDs) are common non-motor symptoms in Parkinson's disease (PD) and associated with significant psychiatric morbidity and reduced quality of life. The prognostic nutritional index (PNI) reflects both nutritional and immune status. However, the relationship between PNI and ICDs in early-stage PD remains unknown. Methods This cross-sectional study included 1,302 early-stage PD patients (Hoehn and Yahr stages 1–3) from the Parkinson's Progression Markers Initiative (PPMI) database. Logistic regression models were constructed with sequential adjustment for demographic, clinical, neuropsychiatric, metabolic, and laboratory covariates. Sensitivity analyses included complete-case analysis, exclusion of participants with abnormal liver or renal function, and propensity score-based methods (IPTW, SMRW, PA). Receiver operating characteristic (ROC) curves, net reclassification improvement (NRI), and integrated discrimination improvement (IDI) were calculated to assess incremental predictive value. Results The overall prevalence of ICDs was 22.6% (294/1,302). In the fully adjusted model, each 1-unit increase in PNI was associated with 5% lower odds of ICDs (OR = 0.95, 95% CI: 0.92–0.98, P = 0.003). Compared with the lowest PNI tertile (T1), the highest tertile (T3) showed 34% reduced odds of ICDs (OR = 0.66, 95% CI: 0.46–0.94, P = 0.023), with a significant dose-response trend (P for trend = 0.025). Subgroup analyses revealed no significant interactions in any strata. Adding PNI to the baseline model significantly improved category-free reclassification (continuous NRI = 0.14, P = 0.03404; IDI = 0.0069, P = 0.00497), although the increase in discrimination was modest and non-significant (C-statistic from 0.714 to 0.720, P = 0.223). All sensitivity analyses confirmed the robustness of these association. Conclusions Higher PNI is independently associated with lower odds of ICDs in early-stage PD patients. PNI, a simple and readily available composite marker of nutritional and immune status, may serve as a valuable adjunctive tool for discriminating PD patients with higher odds of prevalent ICDs. Prospective longitudinal studies are warranted to establish causality and explore potential nutritional or immunomodulatory interventions.