To evaluate the sensitivity and specificity of magnetic resonance imaging (MRI) in detecting erosions, bone edema, and synovitis in the metacarpophalangeal and wrist joints for rheumatoid arthritis (RA).
MRI scans of bilateral hands and wrists of 40 healthy subjects and 40 RA patients were performed using 0.2 T extremity-MRI and read blindly using a modified RA MRI (RAMRIS) system (no contrast injection, imaging in 1 plane only). To determine interreader reliability, images of 10 randomly selected subjects were read independently by a musculoskeletal radiologist.
A total of 3360 bones were evaluated. Patients with RA had significantly more erosions as well as higher scores for bone edema and synovitis than healthy subjects. Age had a significant effect on the number of erosions in both groups. However, when disease duration was factored in, age became insignificant in RA patients. Erosion number correlated with positive rheumatoid factor and higher C-reactive protein values. The intraclass correlation coefficient between the 2 readers was 0.76 for individual joints and 0.88 for total scores. When having a single erosion was used as a positive test for RA, the sensitivity of this test was 90%, but the specificity was only 35%. Presence of bone edema provided 65% sensitivity and 82.5% specificity. Eliminating the lunate from scoring for bone edema increased the specificity to 87.5% while decreasing the sensitivity to 62.5%.
While MRI is a highly sensitive tool for identifying and tracking the progression of erosions, erosions detected by MRI with measures commonly used in a rheumatologist's office (no contrast, imaging in 1 plane) provide low specificity for RA. Bone marrow edema is the most specific MRI lesion for RA in this setting.