Background/Purpose: In daily practice, the diagnostic work-up of patients with possible axial spondyloarthritis (axSpA) starts with clinical and laboratory data. In many patients MRI and/or X-rays of the sacroiliac joints (MRI-SIJ and X-SIJ) is performed to be able to diagnose patients with confidence. We investigated the contribution of imaging (MRI-SIJ and X-SIJ) in making a final diagnosis with confidence.

Methods: All patients with chronic back pain (≥3 months, but ≤2 years, onset ≤45 years) in the SPondyloArthritis Caught Early (SPACE)-cohort in our clinic underwent a diagnostic work-up according to a fixed protocol. First, medical history, physical examination and laboratory assessments, including HLA-B27 typing, were performed. Based on this information, an experienced rheumatologist diagnosed all patients as either SpA or no-SpA with a level of confidence (scale 0 (not confident at all) to 10 (very confident)). Second, imaging (MRI-SIJ and X-SIJ) was performed and a diagnosis was recorded by the same rheumatologist with a new level of confidence. For the analyses, cut-off values of ≤5 (not confident) and ≥6 (confident) were used.

Results: The results are presented in the table. In 52/157 of the patients (33%), the rheumatologist was confident about the diagnosis, either SpA (n=31) or no-SpA (n=21), based on clinical and laboratory data only. Imaging was positive in 32/157 patients (20.4%). In 3/157 patients (1.9%) the rheumatologist was confident about the diagnosis no-SpA, but revised the diagnosis into confident SpA after imaging. In 9/157 patients (5.7%) the rheumatologist reduced the level of confidence about the diagnosis SpA after imaging was performed, since imaging was negative. In 105/157 of the patients (67%), the rheumatologist was not confident about the diagnosis. After performing imaging, the rheumatologist was confident about the diagnosis in 73/105 patients: SpA in 21/105 (20%) patients and no-SpA in 52/105 (50%) patients. In the remaining 32/105 patients (30%) imaging did not change confidence, nor diagnosis.

Conclusion: Imaging (MRI-SIJ and/or X-SIJ) is useful for the rheumatologist in the large majority of patients with possible axSpA, except for the patients in which the rheumatologist is confident about the diagnosis of SpA before imaging.