IL-6 serum levels are elevated in Parkinson's disease patients with fatigue compared to patients without fatigue

To investigate the influence of interleukin-6 (IL-6) and soluble tumor necrosis factor receptors (sTNFR) in fatigued Parkinson's disease (PD) patients. Forty-four PD patients were evaluated, and fatigue was assessed with the Parkinson Fatigue Scale. Logistic regression analysis was used to evaluate the contribution of disease severity scores and cytokine levels on fatigue scores. A receiver operating characteristic (ROC) curve was used to evaluate the diagnostic values of IL-6 in fatigue. Fatigued PD patients had worse cognitive function and depressive symptoms. These patients had worse PD signs and symptoms, displayed more advanced stages of PD, and had greater functional dependence. There was a significant difference in IL-6 serum levels (p = 0.026), but there was no difference in sTNFR levels. Total scores on the Unified Parkinson Disease Rating Scale (β = 1.108; p = 0.004) and IL-6 levels (β = 12.843; p = 0.020) were found to be significant predictors of fatigue scores. A ROC curve revealed that IL-6 concentrations of 1.18 pg/ml represented the best cut-off value for detecting fatigue (sensitivity of 0.941 and specificity of 0.704). Fatigued PD patients have poor clinical outcomes and elevated IL-6 serum levels when compared with non-fatigued patients. These results suggest that IL-6 may play a role in the pathophysiology of fatigue in PD.