MRI Better Than Expected for Spondyloarthritis Diagnosis

MRI has much greater diagnostic utility for patients with spondyloarthritis (SpA) than was documented previously. Low-grade acute and structural sacroiliac (SI) joint lesions may be present in patients with nonspecific back pain and healthy persons.

Weber and associates evaluated T1-weighted and short tau inversion recovery MRI scans of the SI joints obtained from patients 45 years or younger with ankylosing spondylitis (AS), preradiographic inflammatory back pain (IBP), or nonspecific back pain as well as healthy controls. Bone marrow edema, fat infiltration, erosion, and ankylosis were recorded according to standardized definitions. Sensitivity, specificity, and positive and negative likelihood ratios for the diagnosis of SpA were calculated on the basis of global assessment of the MRI scans.

Diagnostic utility was high for patients with AS and those with preradiographic IBP. For patients with IBP, detection of bone marrow edema alone enhanced sensitivity but reduced specificity. With detection of erosions, sensitivity was further enhanced; specificity did not change. A single lesion of the SI joint was seen in up to 27% of controls.

The authors noted that future studies focusing on standardized evaluation of SI joint lesions should address the contribution of structural SI joint damage to diagnosis in early SpA.