Spinal inflammation lesions as detected by magnetic resonance imaging in patients with early ankylosing spondylitis are more often observed in posterior structures of the spine

Objective. To study the localization and extent of spinal inflammation in patients with AS in detail. Methods. This cross-sectional study used standardized clinical tools and MRI, including T1 and T2 fat saturation sequences in both sagittal and axial planes. A simple method of analysis of MRI changes was performed using the principle of `yes/no' to calculate the changes in vertebral body and posterior structures of spine, including costovertebral and costotransversal joints. Results. Consecutive patients with AS (n = 29), who fulfilled the modified NY criteria, were examined by MRI: 67% male, 93% HLA-B27-positive, median age 27.5 (18-49) years, median disease duration 7.5 (1.5-24) years. Inflammatory back pain (IBP), median duration 36 (1-240) months, with a mean intensity of 40mm on a visual analogue scale (20-100) was present in 26 patients (89.7%), and the Bath AS Disease Activity Index (BASDAI) was>40 in 21 patients (72.4%). MRI evidence of spinal inflammation at any site was found in 27 patients (96.5%), whereas radiographic changes were only seen in 6.9% (P<0.05). Patients with a short history of IBP (n = 11) had significantly more lesions in posterior spinal structures than in vertebral bodies: 90.9 vs 27.2%, respectively (P<0.003). Isolated changes in posterior spinal structures were seen in eight of these patients (72.7%), whereas, in contrast, patients with a longer history of IBP (n = 18) had significantly more inflammation in vertebral bodies: 88.9 vs 27.2%, respectively (P<0.01). Conclusions. Inflammatory MRI lesions in early AS are seen more often in posterior structures of the spine. This may be relevant for the diagnosis of early AS and the early detection of inflammatory spinal involvement.