Objective: To determine the effect of methotrexate (MTX) on plasma levels of interleukin (IL)-6 and tumor necrosis factor (TNF)-α and to investigate their associations with clinical and radiographic responses in patients with early rheumatoid arthritis (RA). Methods: Sixty-two untreated RA patients with the disease duration of ≤36 months in whom MTX was initiated were consecutively identified in our prospective RA cohort and included in this study. Concomitant use of prednisolone and synthetic disease-modifying anti-rheumatic drugs with MTX was allowed, but patients who used biological agents were excluded. Plasma IL-6 and TNF-α levels were measured at the time of diagnosis (baseline) and 1 year later. The relationships of the clinical and radiographic data with plasma levels of IL-6 and TNF-α were analyzed. Results: The median age of the patients was 57 years, 49 patients were female, and the median disease duration was 3 months. Forty-six (74.2 %) patients were anti-cyclic citrullinated protein antibody-positive. Serum C-reactive protein (CRP), plasma IL-6, and DAS28 decreased significantly (p <0.001) after MTX treatment, but plasma TNF-α did not. Radiographic progression was significantly correlated with disease activity score and plasma IL-6 levels but not with CRP or TNF-α after MTX treatment. Patients with plasma IL-6 level above 4.03 pg/ml showed clinically relevant radiographic progression with a sensitivity of 91.7 % and a specificity of 88.0 %. Conclusion: In this early RA cohort, we demonstrated a significant (p <0.001) reduction of plasma IL-6, but not TNF-α, during MTX treatment. The post-treatment IL-6 level was a strong indicator of radiographic progression.
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