Serum interleukin 6 levels are associated with depressive state of the patients with knee osteoarthritis irrespective of disease severity

This cross-sectional study investigated the prevalence of depressive state and association between depressive state and serum interleukin (IL)-6 levels in knee osteoarthritis (OA) patients. A total of 115 painful knee OA patients were enrolled and divided into two groups according to the radiographic OA severity. Pain was evaluated using a visual analog scale (VAS). Depressive state was assessed by the self-rating depression scale (SDS). Serum IL-6 levels were also measured. Pearson’s correlation coefficient was used to assess the correlation between the variants tested, and logistic regression analysis was used to identify factors associated with the depressive state. Fifty-two percent of the patients had an SDS score of ≥ 40, which is indicative of the depressive state. The pain VAS score (r = 0.22, p = 0.02) and serum IL-6 level (r = 0.31, p < 0.01) were independently associated with the SDS score of all early-stage knee OA patients (Kellgren-Lawrence [K/L] grade 2). However, only the serum IL-6 level was independently associated with the SDS scores of advanced-stage knee OA patients (K/L grades 3 and 4, r = 0.36, p < 0.01). A logistic regression analysis revealed that serum IL-6 level was the variable for the SDS score [odds ratio 1.41 (95% confidence interval 1.03–1.94, p < 0.03)]. Approximately half of the knee OA patients were found to be in the depressive state, and their serum IL-6 levels to be associated with the depressive state, irrespective of OA severity.