Background:Spondyloarthropathies (SpA) including ankylosing spondylitis are characterized by inflammatory arthritis involving the spine and peripheral joints. Bone SPECT/CT is in the spotlight as it can reflect the current level of inflammation.Objectives:We aimed to investigate the diagnostic performance of bone SPECT/CT for axial SpA (axSpA) at the level of sacroiliac joints.Methods:Patients with low back pain who had undergone SPECT/CT of the SI joints were selected for inclusion in this study through a retrospective review of medical records from August 2016 and July 2018. We used semi-quantitative scoring methods for SPECT/CT. For visual scoring, a score of 0 was assigned when tracer uptake in the sacroiliac joint was less than that in the sacrum; a score of 1, when equal to that in the sacrum; and a score of 2, when greater than that in the sacrum. A score of 2 was considered positive for the diagnosis of sacroiliitis on SPECT/CT (Figure 1). The diagnosis of axSpA was retained when patients fulfilled the Assessment of SpA International Society criteria.Results:A total of 164 patients were enrolled (34 patients with axSpA). The remaining 130 patients had non-axSpA rheumatic inflammatory disease (n=24), vertebral disk herniation (n=13), avascular necrosis (n=11), and others such as bursitis, and fracture (n=85). The mean age of aSpA (37.8±15.6 years) was lower than controls (49.8±16.4 years) (p<0.001), and axSpA (64.5 %) had more male than others (42.1 %) (p=0.024). The sensitivity, specificity, positive and negative predictive values of bone SPECT/CT for axSpA were 83.9%, 63.2%, 34.7%, and 94.4%, respectively. The bone SPECT/CT maximal score and BASDAI score has positive correlation (r=0.481, p=0.007). The bone SPECT/CT compared with MRI is marginal correlation (k=0.369, p<0.001).Conclusion:In patients with low back pain, the bone SPECT/CT has a high negative predictive value that can exclude AS. In addition, when contraindication in MRI the bone SPECT/CT can be an alternative test.References:[1]Rahul V. Parghane, Baljinder Singh, Aman Sharma, Harmandeep Singh, Paramjeet Singh, and Anish Bhattacharya. Role of 99mTc-Methylene Diphosphonate SPECT/CT in the Detection of Sacroiliitis in Patients with Spondyloarthropathy: Comparison with Clinical Markers and MRI. J Nucl Med Technol 2017; 45:280–28[2]Anuj Jain, Suruchi Jain, w A n i l A g a r w a l, Sanjay Gambhir, Chetna Shamshery, and Amita Agarwal(2015). Evaluation of Efficacy of Bone Scan With SPECT/CT in the Management of Low Back Pain. A Study Supported by Differential Diagnostic Local Anesthetic Blocks. Clin J Pain 2015;31:1054–1059[3]Yong-il Kim, Minseok Suh, Yu Kyeong Kim, Ho-Young Lee and Kichul Shin. The usefulness of bone SPECT/CT imaging with volume of interest analysis in early axial spondyloarthritis. BMC Musculoskeletal Disorders (2015) 16:9[4]Jennifer Saunders, Mel Cusi, and Hans Van der Wall. What’s Old Is New Again: The Sacroiliac Joint as a Cause of Lateralizing Low Back Pain. Tomography (2018) VOLUME 4 NUMBER 2[5]Satoshi Kato, Satoru Demura, Hidenori Matsubara, Anri Inak2, Kazuya Shinmura, Noriaki Yokogawa, Hideki Murakam1, Seigo Kinuya and Hiroyuki Tsuchiya. Utility of bone SPECT/CT to identify the primary cause of pain in elderly patients with degenerative lumbar spine disease. Journal of Orthopaedic Surgery and Research (2019) 14:185[6]Romain De Laroche, Erwan Simon, Nicolas Suignard, Thomas Williams, Marc-Pierre Henry, Philippe Robin, Ronan Abgral, David Bourhis Pierre-Yves Salaun, Frédéric Dubrana, Solène Querellou. Clinical interest of quantitative bone SPECT-CT in the preoperative assessment of knee osteoarthritis. De Laroche et al. Medicine (2018) 97:35[7]Inki Lee, Hendra Budiawan, Jee Youn Moon, Gi Jeong Cheon, Yong Chul Kim, Jin Chul Paeng, Keon Wook Kang, June-Key Chung, and Dong Soo Lee. The Value of SPECT/CT in Localizing Pain Site and Prediction of Treatment Response in Patients with Chronic Low Back Pain. J Korean Med Sci 2014; 29: 1711-1716Disclosure of Interests:None declared.