LAUSR

Background: Clinical joint count assessment is important for detecting synovitis but its reliability is controversial Objectives: This study assessed the correlation between bone scintigraphy and positron emission tomography (PET)-derived parameters in 28 joints with disease activity and compared the reliability of joint counts between bone scintigraphy and clinical assessment in rheumatoid arthritis (RA). Methods: We enrolled 86 patients with active RA who underwent bone scintigraphy, fluorine-18-fluorodeoxyglucose (FDG) PET/CT and disease activity evaluation at the same time. This two-step study involved a development (n=67) and validation (n=19) group. Bone scintigraphy-derived joint assessment were compared with PET/CT derived and clinical joint assessment. Subsequently, we developed a disease activity score (DAS) using bone scintigraphy-positive joints and validated it in an independent group. Results: The number of bone scintigraphy-positive joints in 28 joints was significantly correlated with the swollen (SJC)/ tender (TJC) joint counts and PET/CT derived joint counts. Intra- and inter-observer reliabilities of bone scintigraphy for the affected joint counts were excellent. Inter-observer reliability between nuclear medicine physicians and rheumatologists was good for SJC/TJC and PET/CT derived joint counts in 28 joints except shoulders. After multivariate analyses including erythrocyte sediment rate (ESR) and patients global assessment (PGA) in addition to bone scintigraphy-derived parameters, bone scintigraphy/DAS was derived as 0.056 × number of bone scintigraphy-positive joints in 28 joints + 0.012 × ESR + 0.030 × PGA. A significant correlation between bone scintigraphy/DAS and DAS28-ESR was confirmed in the validation group (p<0.001). Conclusion: Bone scintigraphy-derived joint assessment significantly correlated with PET/CT derived joint counts. Bone scintigraphy could serve as a sensitive and reliable method for evaluating disease activity in RA patients. References: Lee SJ, Jeong JH, Lee CH et al. Development and Validation of an 18 F-Fluorodeoxyglucose-Positron Emission Tomography With Computed Tomography-Based Tool for the Evaluation of Joint Counts and Disease Activity in Patients With Rheumatoid Arthritis. Arthritis Rheumatol. 2019 Aug;71(8):1232-1240. doi: 10.1002/art.40860. Epub 2019 Jun 17. Disclosure of Interests: None declared