AB1100 PERFORMANCE OF MAGNETIC RESONANCE IMAGING FOR DETECTING SACROILIITIS IN EARLY STAGES OF SPONDYLOARTHRITIS

Background: In view of the limited accuracy of clinical evaluation to recognize sacroiliitis, several imaging techniques such as conventional radiographs, scintigraphy, ultrasound (US), computed tomography (CT) and magnetic resonance imaging (MRI) have been used to examine the sacroiliac joints (SIJ). Objectives: The aim of this study was to assess the performance of MRI for detecting sacroiliitis in early stages of spondyloarthritis (SpA). Methods: This cross-sectional prospective monocentric double-blind study included 57 patients consulting for symptoms suggestive of SpA during more than 3 months between February 2014 and February 2017. Patients with conventional radiograph showing a confirmed sacroiliitis (grade 3 or 4) were not included. After clinical examination and blood sampling, eligible patients underwent MRI of SIJ. MR images were interpreted by 2 experimented musculoskeletal radiologists blinded to clinical and laboratory data. Two professors in rheumatology blinded to radiologists’ conclusions, analyzed clinical data, laboratory tests, HLA typing, X-rays and MRI images and divided the patients into 2 groups: confirmed non radiographic SpA (nr-SpA) or no SpA. This classification was considered as the gold standard when analyzing the results. Results: Fifteen men and 42 women were enrolled. The mean age at inclusion was 39.75 ± 11 years [17-59]. The mean duration from the first symptom was 47 ± 39 months [6.6-180]. Forty-three patients were assessed as nr-SpA (75.4%) and 14 patients as no SpA (24.6%). Thirty-three percent of patients were HLA B27 positive. Totally 22 patients had sacroiliitis at MRI, all of them classified as confirmed nr-SpA. Among the nr-SpA group, MRI showed bone marrow edema (BME) in 34.9% of patients and erosions in 44.2% of patients. Among the patients in whom the diagnosis of SpA was excluded, MRI showed bone marrow edema (BME) in 7% of patients and erosions in 7% of patients. A statistically significant association was observed between the presence of sacroiliitis at MRI and rheumatologists’ diagnosis of SpA (p=0.001). The diagnostic value of MRI lesions is presented in the following table: Conclusion: SIJ MRI had an excellent specificity for the diagnosis of SpA but a moderate sensitivity. Consequently, some patients in early stages of SpA might be missed by MRI. In addition, we found that diagnostic based solely on BME lacked sensitivity. Detection of erosions in addition to BME enhanced sensitivity (from 34.9% to 44.9%) without changing specificity. Indeed, many recent studies have pointed out the importance of considering structural lesions of SIJ in addition to inflammatory lesions [1, 2]. References: [1]Weber U, Lambert RGW, Pedersen SJ, et al (2010) Assessment of structural lesions in sacroiliac joints enhances diagnostic utility of magnetic resonance imaging in early spondylarthritis. Arthritis Care Res 62:1763–1771. https://doi.org/10.1002/acr.20312 [2]Weber U, Jurik AG, Lambert RGW, Maksymowych WP (2016) Imaging in Spondyloarthritis: Controversies in Recognition of Early Disease. Curr Rheumatol Rep 18:58. https://doi.org/10.1007/s11926-016-0607-7 Disclosure of Interests: None declared