Prevalence of inflammatory posterior arch abnormalities on lumbar spine MRI in spondyloarthritis patients compared with low back pain patients

Objectives This study was conducted in order to compare the prevalence of inflammatory posterior arch abnormalities on lumbar spine MRI between axial spondyloarthritis (axSpA) patients and low back pain (LBP) patients. Methods Patients— axSpA patients meeting the 2009 ASAS criteria and chronic LBP patients who had a lumbar spine MRI were selected. MRI— STIR and T1 sagittal images up to T8–T9 were reviewed by two experienced rheumatologists blinded to the diagnosis and clinical data to identify inflammatory posterior arch abnormalities. Analyses— The prevalence of inflammatory posterior arch abnormalities between axSpA and LBP patients was compared. Clinical data were compared in the axSpA group depending on whether or not inflammatory posterior arch abnormalities were present. Results Ninety-five patients were enrolled in each group. The prevalence of all inflammatory posterior arch abnormalities was the same in the axSpA and LBP groups (58% in the SpA group versus 70% in the LBP group, p = 0.1). However, differences in terms of the prevalence of costotransverse joint arthritis, pedicle oedema above L3 and transverse and spinous process oedema were observed between the two groups (axSpA 27% versus LBP 6%, p = 0.0004). Patients with inflammatory posterior arch abnormalities in the axSpA group had a longer disease duration (11 versus 8 years, p = 0.02), higher CRP levels (median 11 versus 3 mg/l, p = 0.0002) and higher prevalence of radiographic sacroiliitis (84 versus 47%, p = 0.001) compared to patients without inflammatory posterior arch abnormalities. Conclusions Costotransverse arthritis, pedicle oedema and transverse process oedema are more frequent in axSpA patients than LBP patients, on lumbar spine MRI depicting TH9-S1. Key Points • MRI pedicle oedema above L3, transverse process oedema, spinous process oedema or costotransverse arthritis is more frequently observed in axial spondyloarthritis (SpA). • SpA patients with at least one MRI inflammatory lesion on the posterior arch had higher clinical activity scores and biological inflammation. • Facet joint arthritis was more common in patients with chronic low back pain.