Background In recent years, the treatments of rheumatoid arthritis (RA) patients were rapidly developed and many biological drugs, such as tumor necrosis factor (TNF) inhibitors, were newly administered. A humanized anti-interleukin-6 receptor (anti-IL-6R) antibody, Tocilizumab (TCZ) is one of these drugs. In the early stage of the TCZ therapies, C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) have the immediate decrease after the initiation of this drug. Therefore, some previous report demonstrated that Disease Activity Score in 28 Joints (DAS28) was inappropriate marker for the assessments of the patients with RA.

Objectives To evaluate whether TCZ suppress the synovitis of RA patients after 3 months of TCZ therapies and whether we can recognize the conventional assessment by DAS28-CRP and SDAI for patients with TCZ treatments at that time.

Methods Fifteen RA patients treated with TCZ were assessed. Positron emission tomography (PET) with 2-[18F]-fluoro-2-deoxy-D-glucose (¹⁸F-FDG) were performed at baseline, 3 months and 6 months after the initiation of the therapies. The maximal SUV (SUVmax) of the bilateral shoulder, elbow, wrist, hip, knee, and ankle joints were summed up (total SUV) and used for the assessment of the FDG uptake as a representative value. Wilcoxon rank-sum test was applied to compare the clinical evaluations between baseline and each observation period. Spearman’s rank correlation test was used to assess the correlation between the Δ SUV and the difference of the clinical parameters.

Results The total SUV were significantly decreased 3 and 6 months after the initiation of TCZ (p<0.001). The ΔSUV, the difference in the SUVmax of the affected 12 joints before and after treatment, was positively correlated with the ΔDAS28-CRP (r=0.639, p=0.01) and ΔSDAI (r=0.618, p=0.014) (3 months), and ΔDAS28-CRP (r=0.811, p<0.001) and ΔSDAI (r=0.707, p=0.003) (6 months).

Conclusions The TCZ might suppress the synovitis of the RA joint 3 months after the initiation of the therapies. The conventional assessment of RA for the TCZ therapies could reflect the true disease activity.

Disclosure of Interest None Declared