Peripheral blood inflammatory cytokines are associated with rapid eye movement sleep behavior disorder in Parkinson’s disease

Previous studies have shown the essential role of inflammation in rapid eye movement (REM) sleep behavior disorder (RBD). However, the association of RBD in Parkinson's disease (PD) with peripheral blood inflammatory cytokines is still unknown. We investigated the relationship between inflammatory cytokines and the clinical characteristics of PD patients with RBD. A total of 153 PD patients and 36 healthy controls were included in this study, and blood plasma was collected. PD patients were classified as PD with RBD (PD-RBD, n = 60) and PD without RBD (PD-nRBD, n = 93). Inflammatory factor levels were compared among the control, PD-RBD, and PD-nRBD groups. The PD-RBD group had significantly higher C-reactive protein (CRP) levels (P < 0.001), monocytes (P = 0.003), and neutrophil-to-lymphocyte ratio (NLR) (P < 0.001), whereas this group has lower lymphocytes levels (P < 0.001) and lymphocyte-to-monocyte ratio (LMR) (P < 0.001) than the PD-nRBD group. Univariate and multivariate logistic regression analysis indicated that LMR (P < 0.0001 odds ratio [OR] = 0.424) was a protective factor, whereas CRP (P < 0.001 OR = 2.326) was a risk factor for the PD-RBD group. PD-RBD patients had lower Montreal Cognitive Assessment (Beijing version) (MoCA) (P < 0.001) and Mini-Mental State Examination (MMSE) (P = 0.039) scores than PD-nRBD patients. Significant differences were found in inflammation levels between PD-RBD and PD-nRBD, suggesting that inflammatory factors are associated with the pathogenesis of RBD in PD patients. Thus, CRP and LMR levels may serve as biomarkers and predict the prognosis of PD patients with RBD.