gms | German Medical Science

Introduction: Diagnosing early axial spondyloarthritis (SpA) is crucial for effective therapeutic intervention. Magnetic resonance imaging (MRI) helps us to diagnose non-radiographic SpA (nr-ax SpA) in an early stage according to the criteria of the imaging arm of the Assessment of Spondyloarthritis International Society (ASAS) classification. Diagnosis of sacroiliitis using MRI has limitations because of the lack of specificity and sensitivity. Several differential diagnoses are well known and should be considered [1]. In our daily practice, anomalies of the lower lumbar spine and the sacrum, such as spondylolysis, dysraphia, or assimilation joints, are often found to be accompanied by MRI changes in the sacroiliac joints (SIJs) corresponding to sacroiliitis.

To investigate the presence of anatomical anomalies of the lower lumbar spine in our cohort of early diagnosed nr-ax SpA patients fulfilling the criteria of ax SpA and show if they cause a difference in the outcome.

Methods: Patients (n=56, age < 45 years, symptom duration 3–24 months) recently diagnosed with sacroiliitis using MRI and meeting the ASAS criteria for axial SpA were followed-up for 2 years (t0-t2) (Becker-Capeller D, et al. Is the course of newly diagnosed axial spondyloarthritis more aggressive than previously thought? SpA.47 (DGRH Congress 2021 virtuell Posterwalk)). We retrospectively analyzed the anatomic anomalies of the lower lumbar spine on MRI and, if available, on radiograph images.

Results: MRI on t0 revealed that 15 (26.7%, one female and 14 males) of 56 patients had anatomical anomalies of the lower lumbar spine, indicating bone marrow edema with clinical ax SpA according to the ASAS classification criteria. Spondylolysis, assimilation joints, and dysraphia were found in 4 (7.1%), 7 (12,5%), and 7 (12.5%) patients, respectively. The presence of HLA-B27 and assessment results (CRP-ASDAS and BASDAI, BASMI) were similar to patients without the mentioned anatomical anomalies. Patients with spondylolysis and dysraphia of the lower spine and those without anomalies displayed similar progression of MRI findings between t0 and t2.

Conclusion: In addition to the well-known noninflammatory causes of sacroiliitis, such as pregnancies or intensive sporting activity, anatomical peculiarities could not be considered noninflammatory reasons. Contrary to the latest literature [2], in our cohort of early ax SpA they are not responsible for non-specific sacroiliitis. No difference in the development to axial SpA was observed when patients with and without anatomical changes were compared.