Lee SJ, et al. - Researchers investigated how positron emission tomography (PET)–derived parameters in 68 joints are correlated with disease activity in patients with rheumatoid arthritis (RA). In addition, they compared the reliability of joint counts between PET with computed tomography (CT) and clinical assessment in these patients. Enrollment of 91 patients with active RA (69 in a development group and 22 in a validation group) who underwent concurrent ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG)–PET-CT and clinical disease activity evaluation, was done. Findings revealed a significant correlation of the number of PET-positive joints (of 28 and 68 joints) with the swollen joint count and tender joint count and the Disease Activity Score (DAS) in 28 joints (DAS28) using the erythrocyte sedimentation rate [DAS28-ESR]. Following multivariate analyses, they derived the PET/DAS including ESR and patient's global assessment of disease activity in addition to PET-derived parameters. The validation group confirmed the significant correlation between the PET/DAS and the DAS28-ESR. These findings support the possible utility of PET-CT as a sensitive and reliable method in the evaluation of disease activity in RA patients and its applicability as a research tool, particularly in clinical trials.