A new low-field extremity magnetic resonance imaging and proposed compact MRI score: evaluation of anti-tumor necrosis factor biologics on rheumatoid arthritis

Magnetic resonance imaging (MRI) is a useful tool for evaluating disease activity and therapeutic efficacy in rheumatoid arthritis (RA). However, conventional whole-body MRI is inconvenient on several levels. We have therefore developed a new low-field extremity MRI (compact MRI, cMRI) and examined its clinical utility. Thirteen RA patients treated with anti-tumor necrosis factor (TNF) biologics were included in the study. The MRI was performed twice using a 0.21-T extremity MRI system. The MRI images were scored using our proposed cMRI scoring system, which we devised with reference to the Outcome Measures in Rheumatology Clinical Trials RA MRI score (OMERACT RAMRIS). In our cMRI scoring system, synovitis, bone edema, and bone erosion are separately graded on a scale from 0 to 3 by imaging over the whole hand, including the proximal interphalangeal joint. The total cMRI score (cMRIS) is then obtained by calculating the total bone erosion score × 1.5 + total bone edema score × 1.25 + total synovitis score. In this study, one patient showed a progression of bone destruction even under low clinical activity, as assessed by the disease activity score on 28 joints (DAS28); however, another patient’s cMRIS decreased concurrently with the decrease in DAS28, with the positive correlation observed between ΔDAS28 and ΔcMRIS (R = 0.055, P < 0.05). We conclude that cMRI and cMRIS are useful for assessing total disease activity and as a method linking MRI image evaluation to clinical evaluation.