Peripheral Iron and Immune Markers Are Associated With Levodopa-Induced Dyskinesia Severity in Parkinson’s Disease

Background Levodopa-induced dyskinesia (LID) is a common motor complication of Parkinson’s disease (PD), yet peripheral biological factors associated with dyskinesia severity remain insufficiently characterized. Systemic inflammation and iron dysregulation have been implicated in PD, but their relationship with LID expression is unclear. We investigated the association between serum ferritin, neutrophil-to-lymphocyte ratio (NLR), lymphocyte-to-monocyte ratio (LMR), and the presence and severity of LID. Methods In this study, 302 patients with idiopathic PD receiving stable levodopa therapy for at least 24 months were evaluated. Dyskinesia severity was assessed in the medication “ON” state using the Unified Dyskinesia Rating Scale (UDysRS). Serum ferritin and complete blood counts were obtained from fasting samples, and NLR and LMR were calculated. Multivariable regression analyses were performed adjusting for age, sex, disease duration, levodopa equivalent daily dose, Hoehn and Yahr stage, motor severity, C-reactive protein, and amantadine use. Results LID was present in 158 patients (52.3%). Patients with dyskinesia had higher median ferritin levels (152 vs. 104 ng/mL, p < 0.001) and NLR (2.8 vs. 2.0, p < 0.001), and lower LMR (3.5 vs. 4.3, p < 0.001) compared with those without dyskinesia. In adjusted analyses, the highest ferritin quartile was associated with greater UDysRS scores (β = 6.4, p < 0.001), as were the highest NLR quartile (β = 4.9, p = 0.001). Conversely, higher LMR was independently associated with lower dyskinesia severity (β=−4.1, p = 0.006). Conclusions. Elevated serum ferritin and altered leukocyte-derived ratios (NLR, LMR) were independently associated with increased levodopa-induced dyskinesia severity in Parkinson’s disease. These biomarkers may reflect systemic biological processes linked to dyskinesia burden and warrant further evaluation in longitudinal studies.