MRI of the sacroiliac joints in patients with moderate to severe ankylosing spondylitis

OBJECTIVE. The objectives of our study were to evaluate whether MRI findings of the sacroiliac joints are able to distinguish between active and inactive disease in patients with established ankylosing spondylitis and to determine whether these findings correlate with markers of clinical activity, disease duration, severity, and degree of radiographic damage. MATERIALS AND METHODS. Eighteen patients with symptomatic moderate to severe ankylosing spondylitis were evaluated. MRI of the sacroiliac joint (1.5 T) was performed using fat-saturated T2-weighted, T1-weighted, STIR, and fat-saturated contrast-enhanced T1-weighted sequences. The sacroiliac joints were evaluated by two radiologists for enhancement, subchondral bone marrow edema, erosions, and subchondral fatty marrow infiltration. Findings on MRI were analyzed for correlation with multiple clinical characteristics and measures of disease activity, including radiographic scoring. RESULTS. In 17 patients, MRI showed abnormal findings of the sacroiliac joint. Ten patients showed active disease on MRI as measured by abnormal enhancement and subchondral bone marrow edema. Disease activity detected using MRI correlated in a positive fashion with only C-reactive protein (CRP) level. There was no correlation with the other measures of disease activity or with disease duration. In 14 patients, fatty subchondral bone marrow was detected on MRI. These changes were seen in patients with active and chronic disease and correlated with higher radiographic scores but not with disease duration or markers of disease activity. CONCLUSION. Contrast-enhanced MRI of the sacroiliac joint is sensitive in depicting sacroiliitis in patients with established ankylosing spondylitis. Subchondral edema and enhancement correlate with high CRP levels. Subchondral fatty bone marrow changes were seen in both active and chronic sacroiliitis and are correlated with higher radiographic scores; these changes may be a marker of more advanced disease.