Background/Purpose: A humanized anti-interleukin-6 receptor (anti-IL-6R) antibody, tocilizumab (TCZ), is one of the biologics and the C-reactive protein (CRP) level and erythrocyte sedimentation rate (ESR) immediately decrease after the initiation of TCZ therapy. Therefore, it has been proposed that the Disease Activity Score in 28 Joints (DAS28) is an inappropriate marker for assessing the effectiveness of TCZ therapy for RA patients. In fact, clinical physicians are sometimes confused as to how to judge the efficacy of TCZ therapy. Positron emission tomography (PET) with 2-[18F]-fluoro-2-deoxy-D-glucose (18F-FDG) can be used to precisely recognize an increase in synovitis in affected joints, imaging studies with ¹⁸F-FDG PET have been performed to assess the metabolic activity of synovitis in RA patients and evaluate the disease activity of RA. Hence, in the present study, we evaluated whether TCZ suppresses synovitis in RA patients after three or six months of treatment and whether conventional assessments of the DAS 28, DAS28-CRP, simplified disease activity index (SDAI) and clinical disease activity index (CDAI) for patients treated with TCZ reflect the improvements in inflammation observed on ¹⁸F-FDG PET.

Methods: Seventeen patients (5 males, 12 females; average age: 59.9 ± 11.7 (30-82) years) were enrolled in this study. All patients were diagnosed according to the American College of Rheumatology (ACR) criteria revised in 1987 and had a history of a clinically inadequate response to previous treatment with non-biologic disease modifying antirheumatic drugs (DMARDs), including methotrexate (MTX) and biologic agents, including TNF inhibitors only. ¹⁸F-FDG PET was performed at baseline and three and six months after the therapy. The maximum SUV (SUVmax) of the bilateral shoulder, elbow, wrist, hip, knee and ankle joints were totaled (total SUV) and used to assess the degree of FDG uptake as a representative parameter. Wilcoxon’s signed-rank sum test was used to assess differences in the effects of treatment. Spearman’s rank correlation test was applied to test for correlations between the different parameters recorded in this study.

Results: The disease activity scores of the DAS 28, DAS28-CRP, SDAI and CDAI, and total SUV were significantly decreased at three months after the initiation of TCZ. The disease activity and total SUV scores were also found to be further decreased at six months compared to baseline. The ΔSUV, the differences in the total SUV at baseline and three/ six months after treatment, positively correlated with the ΔDAS28 (r = 0.615 p = 0.009/ r = 0.775 p < 0.001), ΔDAS28-CRP (r = 0.696, p = 0.002/ r = 0.828, p < 0.001), ΔSDAI (r = 0.652, p = 0.005/ r = 0.686, p = 0.002) and ΔCDAI (r = 0.662, p = 0.004/ r = 0.711, p = 0.001) for each period.

Conclusion: A reduction in the FDG uptake was observed at three months after the initiation of TCZ therapy. Our results indicate that conventional parameters of TCZ efficacy in RA patients match the disease activity estimated on ¹⁸F-FDG PET. ¹⁸F-FDG PET can be used to evaluate the response of RA patients to TCZ therapy.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/efficacy-of-tocilizumab-therapy-in-patients-with-rheumatoid-arthritis-based-on-fdg-petct/