Finger joint synovitis in rheumatoid arthritis: quantitative assessment by magnetic resonance imaging

Objective. To assess quantitatively, by magnetic resonance imaging (MRI), the synovial membrane volume in second to fifth metacarpophalangeal (MCP) joints in patients with rheumatoid arthritis and healthy controls, and to compare the synovial membrane volumes with a more easily obtained semi-quantitative score for hypertrophic synovial membrane. Patients and methods. MCP joints of the dominant hand of 37 patients and five controls were examined clinically and by MRI. Laboratory assessments were performed. Results. Median synovial membrane volumes were considerably larger in clinically active rheumatoid arthritis (RA) joints (e.g. 0.97 ml in the second MCP joint) than in clinically inactive joints (0.54 ml) and control joints (0.04 ml). Nevertheless, group distributions overlapped and marked volume differences were found within clinically uniform groups. The semi-quantitative score was highly correlated with the synovial volumes (Spearman rho = 0.79; P < 0.00001). Synovial membrane volumes were poorly related to the presence of rheumatoid factor and to laboratory markers of inflammation. Conclusion. These findings suggest that synovial membrane volumes, as determined by MRI, in finger joints are related to clinical signs of synovitis, but also that the volumes may vary more than what can be accounted for by the clinical appearances. A semi-quantitative score may be sufficient for more routine purposes.