Distribution of spinal damage in patients with axial spondyloarthritis as assessed by MRI: a prospective and blinded study

Axial spondyloarthritis (SpA) leads to structural bone lesions in every part of the vertebral column. These lesions are only partially visualized on conventional radiographs, omitting posterior parts of the vertebral column and the thoracic spine, that may nevertheless contribute to impaired spinal mobility and function in patients with axial SpA. In this prospective and blinded investigation, we assessed the distribution of structural spinal lesions using magnetic resonance imaging (MRI) of the whole spine in 55 patients with axial SpA classified according to the Assessment in Spondyloarthritis International Society (ASAS) criteria. After assessment of spinal mobility and function two blinded radiologists independently evaluated MRIs of 23 vertebral units in every patient. Non-parametric statistical methods, Spearman‘s correlation and linear regression models were used to analyze structural lesion distribution and the relationship with clinical spinal mobility and function parameters. In 55 patients with axial SpA (13 females, average disease duration 14.9 years) 657 ventral and 139 dorsal vertebral body structural bone lesions and, notably, 534 facet joint lesions could be visualized. The median number of lesions per patient was higher in the thoracic (8.5, range 1.0–41.0) than in the lumbar (7.5, range 0.0-27.5) and the cervical spine (3.5, range 0.0-24.5). A negative correlation was noted between the number of osteoproliferative structural bone lesions and impairment of spinal mobility and function in univariate, but not in multivariate analyses. MRI of the whole spine revealed a high prevalence of lesions in dorsal parts of the vertebral column and in the thoracic spine in patients with axial SpA that may not be adequately visualized on conventional radiographs. These findings could further contribute to a better understanding of reduced mobility of the spine typically associated with axial SpA and assist diagnostics.