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

Abstract

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 x 1.5 + total bone edema score x 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 DeltaDAS28 and DeltacMRIS (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.

Fig. 1

Sites evaluated in calculating the compact magnetic resonance imaging (MRI) score. In this scoring system, 23 bones and 16 joints were evaluated. Pisiforme was excluded from the wrist bone evaluation. Bone erosion and edema were evaluated in 32 sites, and synovitis was evaluated in 11 sites. The score calculation is provided in detail in Table 2

Fig. 2

Serial changes in disease activity score on 28 joints (DAS28) and compact MRI score (cMRIS) between first (1st) and second (2nd) MRI examinations. All patients except one had a good or moderate response to the biologics, and none showed increased disease activity. The cMRIS scores generally decreased or remained constant. However, one patient of the infliximab group showed an increase in cMRIS score even under low disease activity (dotted line)

Fig. 3

Relationship between changes in the cMRIS value (ΔcMRIS) and changes in the DAS28 (ΔDAS28). ΔcMRIS and ΔDAS28 are the differences between the first and the second images. A positive correlation was observed between two evaluations (R = 0.55, P < 0.05)