Reappraisal of bone scintigraphy as a new tool for the evaluation of disease activity in patients with rheumatoid arthritis

We aimed to compare the reliability of bone scintigraphy (BS) and fluorine-18-fluorodeoxyglucose (F-18-FDG) positron emission tomography (PET)-derived parameters in the detection of active arthritis in 28-joint areas and evaluate the reliability of joint counts between BS and clinical assessment in patients with rheumatoid arthritis (RA). We enrolled 106 patients (67 in the development group and 39 in the validation groups) with active RA who underwent BS, F-18-FDG PET/computed tomography (CT), and clinical evaluation of disease activity. We compared the results of BS-derived joint assessment with those of PET-derived and clinical joint assessments. Subsequently we developed a disease activity score (DAS) using BS-positive joints and validated it in an independent group. The number of BS-positive joints in 28-joint areas significantly correlated with the swollen /tender joint counts (SJC/TJC) and PET-derived joint counts. A BS uptake score of 2 (strong positive) was significantly more sensitive compared with a BS uptake score of 1 (weak positive) in detecting a PET-positive joint among the 28-joints. After conducting multivariate analyses including erythrocyte sediment rate (ESR) and patient global assessment (PGA) in addition to BS-derived parameters, BS/DAS was obtained as follows: 0.056 x number of BS-positive joints in 28 joints + 0.012 x ESR + 0.030 x PGA. A significant correlation between BS/DAS and DAS28-ESR was confirmed in the validation group. Strong positive uptake of BS is sensitive and reproducible for the detection of active joints, and can complement the clinical assessment of disease activity in RA.