Association of neutrophil-to-lymphocyte ratio with incidence and disease progression in Parkinson's disease

Background: The neutrophil-to-lymphocyte ratio (NLR) is widely regarded as a proxy for system inflammation. The previous study indicated that the NLR might be higher in Parkinson’s disease (PD) compared to healthy controls (HC). The study aimed to assess the role of system inflammation indicated by NLR in the incidence and progression of PD. Methods: We included participants from the longitudinal population-based cohort, UK Biobank, to analyze the association of NLR and the risk of PD. We conducted the Cox proportional hazards analyses as the primary analysis to determine the association between baseline NLR value and the risk of PD in UK Biobank. Then we further used data from a disease-specific longitudinal cohort, Parkinson’s Progression Markers Initiative (PPMI), to evaluate the differences between individuals with higher PD risk, and early-stage PD patients in the values of NLR. Patients with PD were divided into two groups according to the median value of NLR (2.35). Linear mixed models (random intercept and random slope) were used to evaluate the relationship between the high/low NLR groups and the disease progression. Results: A number of 288837 participants from UK Biobank were included and 1429 were diagnosed with incident PD. Among them, higher NLR was associated with an increased risk of incident PD in HC (per SD increment hazard ratio [HR], 1.041; P < 0.001). A total of 349 early-stage PD patients, 438 individuals with higher PD risk, and 207 HC were included from PPMI. PD patients and individuals with higher PD risk had a significantly higher NLR compared to healthy controls. Higher NLR group was associated with a faster deterioration of the Montreal Cognitive Assessment score in PD patients in two years (β [SE] = -0.225 [0.080], P = 0.005). Conclusion: In conclusion, increased NLR in HC was linked with a higher risk of incident PD, and higher NLR was associated with a faster cognitive decline in PD patients, which indicated that inflammation was involved in the incidence of PD and the cognitive decline in early-stage PD.