Serum interleukin-6 in seropositive rheumatoid arthritis and response to tocilizumab: An observational study.

Objective: There is no clinically useful biomarker as a predictor of response to any class of biological disease-modifying antirheumatic drugs (bDMARD). Serum interleukin-6 (IL-6) has a major role in the pathogenesis of rheumatoid arthritis (RA) and its serum level in patients of RA may predict response to treatment with IL-6 receptor (IL-6R) antagonist tocilizumab.

Methods: Biological DMARD naïve patients of seropositive RA, fulfilling American College of Rheumatology/European League Against Rheumatism classification criteria 2010, were treated with 06 doses of tocilizumab (8mg/kg) at monthly interval. Baseline and post-treatment serum IL-6 levels were measured and correlated with response to treatment measured by disease activity score-28 joints erythrocyte sedimentation rate (DAS28 ESR) after treatment.

Results: The study included 34 patients and 26 (70%) of them achieved DAS-28 remission (DAS28 ESR < 2.6). The baseline serum IL-6 did not correlate with post-treatment DAS28 ESR (R -0.197, P = .264). Though, statistically not significant (P = .085) more patients with comparatively lower baseline serum IL-6 attained DAS28 remission (16 out of 17, P = .085). There was an increase in the serum IL-6 level (median 40.5pg/ml [IQR 130.2] to 72.6pg/ml [IQR 162.5]) after tocilizumab treatment and the change in IL-6 level also did not correlate with post-treatment DAS28 ESR (R -0.240, P = .172).

Conclusion: Higher number of patients with comparatively lower serum IL-6 level attained DAS28 remission in this study; however, it was not statistically significant. It requires further evaluation in larger studies to make any conclusion on the role of serum IL-6 as a predictor of response to tocilizumab in seropositive RA.