Association between inflammatory markers (SII and SIRI) and anxiety levels in Parkinson's disease.

Background: Parkinson's disease (PD) is a progressive neurodegenerative disorder frequently associated with anxiety, which can significantly impair patients' quality of life. Emerging evidence suggests that systemic inflammation may contribute to the development of anxiety in PD. The Systemic Immune-Inflammation Index (SII) and Systemic Inflammation Response Index (SIRI) are composite biomarkers reflecting systemic inflammatory status. However, the relationship between these inflammatory markers and anxiety levels in PD patients remains to be elucidated. Objective: To investigate the association between SII and SIRI and anxiety levels in PD patients. Methods: This cross-sectional study utilized data from the PPMI database, including 1,289 PD patients. Anxiety levels were assessed using the State-Trait Anxiety Inventory (STAI), with separate evaluations for state and trait anxiety. Linear regression analyses were performed to assess the associations between SII, SIRI, and anxiety levels. Curve fitting analysis was conducted to explore potential non-linear relationships, and sensitivity and subgroup analyses were performed to verify the robustness of the results. Results: Linear regression analyses showed significant positive associations between SII and overall STAI scores [β = 0.34 (95% CI 0.07 - 0.6), p = 0.014], STAI-state [β = 0.21 (95% CI 0.06 - 0.36), p = 0.005], and a non-significant association with STAI-trait [β = 0.13 (95% CI - 0.01 - 0.26), p = 0.073]. SIRI was significantly associated with overall STAI scores [β = 0.16 (95% CI 0.04 - 0.27), p = 0.008], STAI-state [β = 0.1 (95% CI 0.04 - 0.17), p = 0.002], and a non-significant association with STAI-trait [β = 0.06 (95% CI 0 - 0.12), p = 0.068]. Curve fitting analysis revealed no significant non-linear relationships between SII/SIRI and anxiety levels, indicating a linear positive correlation. Sensitivity and subgroup analyses confirmed the robustness of these findings. Conclusion: Our study demonstrates a significant positive linear association between SII and SIRI and anxiety levels, particularly state anxiety, in PD patients. These findings suggest that systemic inflammation may play a role in the development of anxiety in PD and highlight the potential utility of SII and SIRI as biomarkers for anxiety in this population. Future longitudinal studies are warranted to explore the causal relationship and potential therapeutic implications.