THU0393 Increased 18F-Fluoride Uptake Lesions at Vertebral Corners on Positron Emission Tomography Predict New Syndesmophytes Development in Ankylosing Spondylitis

Background 18F-fluoride uptake on positron emission tomography (PET) represents osteoblastic activity. Previous cross-sectional studies showed that increased 18F-fluoride uptake lesions at vertebral corners were associated with both inflammation and structural changes on magnetic resonance imaging (MRI) and radiography, respectively, in patients with ankylosing spondylitis (AS) 1,2 . But, longitudinal studies that investigated the association between increased 18F-fluoride uptake lesions and future syndesmophytes formation are lacking. Objectives We aimed to demonstrate that increased 18F-fluoride uptake lesions on PET predict the development of new syndesmophytes. Methods In 12 patients with AS, 18F-fluoride PET-MRI (Philips Healthcare, Cleveland, OH, USA) was performed at baseline and radiography was performed at baseline and 2 years. We recorded 18F-fluoride uptake lesions on PET, acute (type A) and advanced (type B) corner inflammatory lesions (CILs) and fat lesions on MRI and syndesmophytes on radiography. An increased 18F-fluoride uptake lesion was defined as an uptake greater than the uptake in the adjacent normal vertebral body (Figure 1). Results Of 231 anterior vertebral corners without syndesmophyte at baseline, 13 type A CILs (5.5%), 2 type B CILs (0.9%) and 20 fat lesions (8.7%) on MRI and 6 increased fluoride uptake lesions (2.6%) on PET were observed. After 2 years, 16 new syndesmophytes (6.9%) in 8 AS patients (66.7%) occurred. New syndesmophytes developed significantly more frequently in anterior vertebral corners with increased 18F-fluoride uptake lesions (50%) or fat lesions (25%) at baseline, as compared with those without either feature (5.8% and 5.2%, respectively). In generalised linear latent mixed models after adjusting within-patient correlation, baseline increased 18F-fluoride uptake lesion significantly predicted the development of new syndesmophytes (OR=20.6, 95% CI=2.7–156.1, p=0.003). Fat lesions were also associated with new syndesmophytes development (OR=9.3, 95% CI=2.1–40.2, p=0.003), but this association was not observed in CILs. Conclusions Our findings indicate that increased 18F-fluoride uptake lesions can predict future new syndesmophytes formation in patients with AS. 18F-fluoride PET may be used to estimate structural damage in these patients. References Lee SG et al. Assessment of bone synthetic activity in inflammatory lesions and syndesmophytes in patients with ankylosing spondylitis: the potential role of 18F-fluoride positron emission tomography-magnetic resonance imaging. Clin Exp Rheumatol 2015;33:90–7. Buchbender C et al. Hybrid 18F-labeled Fluoride Positron Emission Tomography/Magnetic Resonance (MR) Imaging of the Sacroiliac Joints and the Spine in Patients with Axial Spondyloarthritis: A Pilot Study Exploring the Link of MR Bone Pathologies and Increased Osteoblastic Activity. J Rheumatol 2015;42:1631–7. Disclosure of Interest None declared