Volume: 46 Issue: 1
Year: 2026, Page: 67-75, Doi: https://doi.org/10.51248/v46i1.206
Received: Oct. 12, 2025 Accepted: March 10, 2026 Published: March 17, 2026
Introduction & Aim: Systemic inflammation is implicated in Parkinson's disease (PD) pathogenesis, but evidence regarding peripheral cytokine levels remains inconsistent. This meta-analysis aimed to summarize the available data on peripheral blood cytokine concentrations in PD patients compared to healthy controls (HCs), and investigate key moderator variables that may affect cytokine concentrations. Materials & Methods: A systematic literature search was conducted across multiple electronic databases from August 06 to August 26, 2025. Eligible studies reporting peripheral blood cytokine levels in PD patients and a matched HC group, were included. Data from 100 studies, comprising 7,369 PD patients and 10,978 HCs, were extracted, and the meta-analysis was performed using a random-effects model, with effect sizes expressed as standardized mean differences (Hedges' g). Results: Concentrations of interleukin-6, tumour necrosis factor, interleukin-1 beta, and C-reactive protein were elevated in PD patient’s relative to HCs. In contrast, no significant differences were observed for interleukin-2, interleukin-4, interleukin-8, and interleukin-10. Subgroup analyses revealed that the analytical methodology, sample source (serum, plasma, or cerebrospinal fluid), and geographic origin of the study population significantly influenced effect sizes, whereas patient age, motor severity (UPDRS-III), and disease stage (Hoehn & Yahr) did not demonstrate a significant moderating effect. Conclusion: This meta-analysis confirms a distinct peripheral inflammatory profile in PD, characterized by elevated levels of specific pro-inflammatory cytokines. The findings underscore the potential role of systemic inflammation in PD pathophysiology and highlight methodological and demographic variables as key sources of heterogeneity in the literature, which must be considered in future biomarker studies.
Keywords: Parkinson’s disease; meta analysis; interleukins; cytokines; biomarkers
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