Assessment of Structural Lesions in Sacroiliac Joints Enhances Diagnostic Utility of Magnetic Resonance Imaging in Early Spondylarthritis

Objective. To compare the diagnostic utility of T1-weighted and STIR magnetic resonance imaging (MRI) sequences in early spondylarthritis (SpA) using a standardized approach to the evaluation of sacroiliac (SI) joints, and to test whether systematic calibration of readers directed at recognition of abnormalities on T1-weighted MRI would enhance diagnostic utility. Methods. Six readers independently assessed T1-weighted and STIR MRI scans of the SI joints from 187 subjects: 75 ankylosing spondylitis (AS) and 27 preradiographic inflammatory back pain (IBP) patients, and 26 mechanical back pain and 59 healthy volunteer controls ages <= 45 years. The exercise was repeated 6 months later on a random selection of 30 AS patients and 34 controls after calibration directed at lesions visible on T1-weighted MRI. Specific MRI lesions were recorded according to standardized definitions. In addition to deciding on the presence/absence of SpA, readers were asked which MRI sequence and which type of lesion was the primary basis for their diagnostic conclusion. Results. Structural lesions were detected in 98% of AS patients and 64% of IBP patients. A diagnosis of SpA was based on T1-weighted or combined T1-weighted/STIR sequences in 82% of AS patients and 41% of IBP patients. Calibration enhanced the diagnostic utility of MRI in the majority of readers, especially those considered less experienced; the mean positive and negative likelihood ratios (of 6 readers) were 14.5 and 0.08 precalibration, respectively, and 22.2 and 0.02 postcalibration, respectively. Conclusion. Recognition of structural lesions on T1-weighted MRI contributes significantly to its diagnostic utility in early SpA. Rheumatologist training directed at detection of lesions visible on T1-weighted MRI enhances diagnostic utility.