Objective: To evaluate synovial membrane volumes, effusion volumes, and cartilage and bone erosion scores determined by magnetic resonance imaging (MRI) as markers of disease activity and severity in arthritis.
Methods: Gadolinium-DTPA enhanced MRI of 18 arthritic knees was performed before and 1, 7, 30 and 180 days after intraarticular methylprednisolone injection until clinical relapse. Intraobserver, interobserver, and inter-MRI variations were determined from 2 successive MRI of another 6 knees.
Results: In all knees synovial membrane and effusion volumes decreased within the first posttreatment week (median decrease 49 and 65%, respectively), and remained low during remission. Synovial volumes, but not effusion volumes, increased to pretreatment levels in case of clinical relapse, indicating that synovial volumes were most important to the clinical appearance. The intraobserver + interobserver + inter-MRI variation was maximally 26%. Total volumes and volumes in a selected sagittal slice were highly statistically correlated. The duration of clinical remission in patients with rheumatoid arthritis (RA) was significantly inversely correlated to the pretreatment synovial volume (both total and "one slice" volumes), but not to the effusion volume, MRI or radiography scores of erosions or any clinical/laboratory variables. Cartilage and bone erosions, invisible by radiography, were visualized by MRI. No progressive erosive changes were observed.
Conclusion: MRI-determined synovial and effusion volumes and MRI scores of cartilage and bone erosions are reproducible and may be sensitive measures of disease activity and severity in RA. The synovial volume may rather than the effusion volume determine clinical appearance. Both are influenced by the present inflammatory activity. The pretreatment synovial volume may have predictive value to treatment outcome in RA.