OP0313 TO X-RAY OR NOT TO X-RAY - PRELIMINARY RESULTS OF A COMPARATIVE STUDY ON FIRST-LINE IMAGING IN SUSPECTED AXIAL SPONDYLOARTHRITIS (axSpA)

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Background: According to current recommendations, patients with suspected axial Spondyloarthritis (axSpA) typically undergo initial radiography of the sacroiliac joint (SIJ), followed by magnetic resonance imaging (MRI) if the radiograph is negative [1]. However, X-rays (XR) of the SIJ are known for their low interrater agreement and diagnostic accuracy [2, 3]. Computed tomography (CT) may be used in cases of unclear diagnosis but is not part of the standard imaging pathway. However, since the development of ultra-low-dose techniques that allow for radiation exposure comparable to or lower than XR, CT has gained attention within the rheumatology field. Furthermore, CT serves as the reference standard for structural lesions in many studies [4]. Objectives: To evaluate the diagnostic efficacy of three different imaging pathways starting with XR, MRI, or ultra-low-dose CT of the SIJ in patients with suspected axSpA. Methods: A total of 176 patients with suspected axSpA from the rheumatology department of a university hospital in Germany were randomized into three arms: 1Standard Arm: XR first, followed by MRI if negative, followed by CT if negative. 2MRI-First Arm: MRI first, followed by CT if MRI was negative. 3CT-First Arm: CT first, followed by MRI if CT was negative. X-rays were performed in the Ferguson projection, the MRI protocol followed the European Society of Musculoskeletal Radiology (ESSR) recommendations, and CT was conducted using an ultra-low-dose technique [5]. Positive imaging was defined as the unambiguous identification of active inflammatory (bone marrow oedema according to the updated ASAS definition suggestive of axSpA [6]) or structural lesions (e.g. unequivocal erosion or ankylosis suggestive of axSpA). Images were assessed in consensus reading by two radiologist specialists in musculoskeletal imaging (D.D. with 4 years of experience; T.D. with 12 years of experience) who were blinded for all clinical data. Results: The study included 176 patients with suspected axSpA. The key clinical characteristics were as follows: mean age 38 years (SD 10.58), 58.2% female, mean back pain duration 8.2 years (SD 6.8 years), 53.8% HLA-B27 positive, mean C-reactive protein level 3.66 mg/L (SD 5.66), inflammatory back pain in 70.6% of cases, and mean BMI 25.57 (SD 5.15). •Standard-Imaging Arm (24 patients): XR was positive in 1/24 patients (4.17%). Subsequent MRI was positive in 3/23 patients (12.5%) and negative in the remaining 20 patients. All 20 patients who underwent further CT had negative results. •MRI-First Arm (78 patients): MRI was positive in 19/78 patients (24.36%). Subsequent CT in 59 patients revealed no positive results (0/59). •CT-First Arm (74 patients): Initial CT was positive in 19/74 patients (25.68%). Subsequent MRI, performed in 55 patients, was positive in two patients (3.64%). Figure 1Diagnostic pathways with 1. Standard setting, 2. MRI-first and 3. CT-first. If initial imaging was negative, subsequent imaging according to the approached pathways were performed to determine whether additional positive results could be identified. Conclusion: The standard imaging pathway demonstrated the lowest diagnostic efficacy compared to the MRI-first and CT-first approaches, raising the question of whether the current imaging pathway should be updated. REFERENCES: [1] Mandl P, Navarro-Compán V, Terslev L, Aegerter P, van der Heijde D, D'Agostino MA, et al. EULAR recommendations for the use of imaging in the diagnosis and management of spondyloarthritis in clinical practice. Ann Rheum Dis. 2015;74(7):1327-39. [2] Diekhoff T, Eshed I, Radny F, Ziegeler K, Proft F, Greese J, et al. Choose wisely: imaging for diagnosis of axial spondyloarthritis. Ann Rheum Dis. 2021. [3] Ulas ST, Radny F, Ziegeler K, Eshed I, Greese J, Deppe D, et al. Self-reported diagnostic confidence predicts diagnostic accuracy in axial spondyloarthritis imaging. Rheumatology (Oxford). 2024;63(8):2199-204. [4] Diekhoff T, Hermann KG, Greese J, Schwenke C, Poddubnyy D, Hamm B, et al. Comparison of MRI with radiography for detecting structural lesions of the sacroiliac joint using CT as standard of reference: results from the SIMACT study. Ann Rheum Dis. 2017;76(9):1502-8. [5] Vereecke E, Diekhoff T, Eshed I, Herregods N, Morbée L, Jaremko JL, et al. ESR Essentials: Imaging of sacroiliitis-practice recommendations by ESSR. Eur Radiol. 2024. [6] Lambert RG, Bakker PA, van der Heijde D, Weber U, Rudwaleit M, Hermann KG, et al. Defining active sacroiliitis on MRI for classification of axial spondyloarthritis: update by the ASAS MRI working group. Ann Rheum Dis. 2016;75(11):1958-63. Acknowledgements: NIL . Disclosure of Interests: None declared . © The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.

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