IL6 and Parkinson disease: Existing data on serum or plasma cytokines in PD is limited to a few reports of elevated cytokines (including TNF‐α, IL‐6, IL‐1, and IL‐2) in small cohorts of PD patients (n < 80) compared with controls30, 31, 32, 33 and 2 small cross‐sectional studies reporting association between IL‐6 and motor function34 and TNF‐α and the soluble IL‐2 receptor and nonmotor severity,35 respectively.