Caution: MRI has low specificity for RA

MRI abnormalities that resemble rheumatoid arthritis (RA) pathologies often are found in the metacarpophalangeal and wrist joints of healthy persons. Although MRI is highly sensitive for tracking the progression of erosions, it has low specificity for RA, suggesting caution in the interpretation of joint lesions on MRI, especially in early arthritis.

Olech and coworkers explored the sensitivity and specificity of MRI for detecting erosions, synovitis, and bone edema in the fingers and wrists of 40 patients with RA and 40 controls. Overall, 3360 bones were examined.

The number of erosions correlated with rheumatoid factor seropositivity and C-reactive protein (CRP) level, as well as disease duration. Bone edema also correlated with CRP level. Bone edema, synovitis scores, and the total number of erosions and erosion scores were highly correlated with age, but factoring in disease duration, age was insignificant in persons with RA. The presence of a single erosion was 90% sensitive for RA but only 35% specific. The presence of bone edema was 65% sensitive and 82.5% specific for RA; bone marrow edema is the most specific sole MRI finding for RA.

The authors noted that validation studies of MRI findings in the early diagnosis of RA are needed.