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AB0722 DOES THE ULTRASOUND OF SACROILIAC JOINTS CONTRIBUTE TO THE DIAGNOSIS OF SPONDYLOARTHRITIS?

Background: Although pelvic radiography is a robust imaging modality to detect sacroiliitis, radiographic changes require at least 5 years to develop after symptom onset, hence the increasing interest in new imaging tools in the field of spondyloarthritis (SpA). Whereas the diagnostic utility of magnetic resonance imaging (MRI) and computed tomography (CT) of sacroiliac joints (SIJ) has been extensively studied in many cohorts, the contribution of SIJ ultrasound (US) in the diagnostic of SpA has been little-studied. Objectives: The objective of this study is to assess the performance of SIJ US for detecting sacroiliitis and to determine its sensitivity and specificity in patients with SpA. Methods: Consecutive patients, aged 16 years and over, consulting for symptoms suggestive of SpA (inflammatory back pain, enthesitis or dactylitis…) from February 2014 to February 2017 were enrolled in this cohort. Eligible patients underwent physical examinations, laboratory tests, SIJ US, CT and/or MRIs, following a standardized protocol. Patients with a conventional radiography showing a confirmed sacroiliitis (grade 3 or 4) were not included. The US was considered positive when showing a unilateral or bilateral vascularization (Doppler signals). Then, resistive index (RI) was measured. After analyzing clinical and radiological data and HLA typing, two experienced rheumatologists, blinded to US results, proceeded to the classification of the patients into 2 groups: confirmed SpA or no SpA. Their final diagnosis was considered the gold standard in interpreting the results of US examination. Results: Forty-five patients, 10 men and 35 women, with an average age of 39 years were included. The mean duration of symptoms was 75 months (6 years). A family history of SpA was noted in 2.22% of patients. A personal history of Reiter’s syndrome was noted in 2.22% of patients and of uveitis in 6.66%. Morning stiffness was noted in 60% (n=27) of patients. Good response to nonsteroidal anti-inflammatory drugs (NSAIDs) and to physical activity were respectively reported by 42.22% (n=19) and 57.8% (n=26) of patients. Twenty-seven per cent of the patients were HLA-B27+. Fifty-one per cent of the studied patients fulfilled the aSAS criteria for axial SpA and 46.7% fulfilled the amor criteria. After a follow-up between 2 and 3 years, the diagnosis of SpA was confirmed by the referring rheumatologists in 31 (68.9%) patients and excluded in 14 (31.1%) patients. Among the 31 patients with confirmed SpA, 61.3% (n=19) had a positive US (with a mean RI estimated at 0.75) and 38.7% (n=12) had a normal US. Among the 14 patients in whom SpA was excluded, 50% (n=7) had a positive US (with a mean RI estimated at 0.7) and 50% had a normal US. Sensitivity and specificity of US examination were estimated at 61.3% and 50%. Positive and negative likelihood ratio were estimated at 73% and 36.8%. Association between US findings and rheumatologists’ diagnosis of SpA was not statistically significant (p=0.47). Conclusion: US contribution in the diagnostic of SpA has been little-studied. In our study, although US of SIJ lacked specificity, it has a satisfactory sensitivity and positive likehood ratio. In fact, this tool is more valuable by its positivity which indicates a high probability of sacroiliitis. However, further investigation is needed in order to assess its performance for ascertaining sacroiliitis. Disclosure of interests: None declared