IL6 and Parkinson disease: Considering the influence of age on the levels of neuroinflammatory factors in CSF, we made further correlation analyses between IL-6 level in CSF and age in both PD group and PD-CI group, and find that the coefficients are not significant in both groups (r = 0.184, P = 0.401; r = 0.111, P = 0.731, respectively).