Pos1071 [18f]fluoride pet-ct scans visualize both axial and peripheral bone formation in psoriatic arthritis patients

BackgroundPsoriatic arthritis (PsA) can present with peripheral (i.e. arthritis, enthesitis, dactylitis) and/or axial (spondyloarthritis) manifestations. Positron Emission Tomography (PET) may be a promising imaging technique for detection of whole body disease activity since it combines quantification and picomolar sensitivity for accurate depiction of pathologic processes with anatomical low dose CT imaging as a reference (3, 4). It was recently demonstrated that [18F]Fluoride PET-CT scans can successfully visualize and monitor ankylosing spondylitis disease activity by imaging of bone formation in the axial skeleton (5). Since bone formation is associated with enthesitis and synovitis in PsA, [18F]Fluoride may enable sensitive, whole body detection of disease activity in PsA.ObjectivesTo investigate the feasibility of [18F]Fluoride PET-CT to visualize disease activity of PsA by imaging of bone formation at axial and peripheral sites in PsA patients.MethodsSixteen patients (female 10/16, age 50.6 ±8.9 years) with PsA fulfilling CASPAR criteria and clinically active disease including ≥1 clinically active enthesitis site were included. Clinical disease activity was assessed by swollen joint count/tender joint count 44, MASES and SPARCC. Of each patient, a whole body [18F]Fluoride PET-CT scan at 45 minutes post injection was performed. All scans were dichotomously scored by two board certified readers (blinded for clinical data) for PET-positive lesions in the joints, peripheral enthesis sites and spine. Low dose CT was used for anatomical reference.ResultsOut of 1088 evaluated joints, 109 joints showed PET enhancement, most frequently in the interphalangeal- and metatarsal joints of the feet (14/109, 12,9%) (Figure 1A) and the distal interphalangeal joints of the hands (14/109, 12,9%). Out of 416 evaluated entheseal sites, PET positivity was found at 44 sites, mainly located at the patella tendon insertion (11/44, 25%) (Figure 1B) and the quadriceps tendon insertion (10/44, 22.7%). Of the PET positive joints and entheses sites, respectively 81.1% and 70.5% were not associated with tender or swollen joints and clinical enthesitis, respectively. In 11 out of the 16 patients ≥1 axial PET positive lesion was observed (Figure 1C), most frequently located in the cervical spine (19/49 observed axial lesions, 38.8%). Two patients showed PET enhancement in one sacro-iliac joint (SIJ) without any inflammatory back pain (IBP). Only four out of 15 patients reported IBP and missing data for 1 patient. In two patients clinical dactylitis was observed which was also depicted on PET-CT.Figure 1.[18F]Fluoride uptake in the metatarsal and IP-joints of the feet (A), in the patella tendon (B) and in the spine (C)Conclusion[18F]Fluoride PET-CT scans can visualize disease activity at whole body musculoskeletal manifestations of PsA by demonstrating local bone formation in joints, entheses and the axial skeleton. By sensitive imaging of bone formation at active sites, [18F]Fluoride PET-CT adds information to clinical disease activity, reflected by a high number of clinically negative, PET positive sites on top of concordant findings.References[1]Kaeley GS, Eder L, Aydin SZ, Gutierrez M, Bakewell C. Enthesitis: A hallmark of psoriatic arthritis. Semin Arthritis Rheum. 2018;48(1):35-43.[2]Ogdie A, Coates LC, Gladman DD. Treatment guidelines in psoriatic arthritis. Rheumatology (Oxford). 2020;59(Suppl 1):i37-i46.[3]von Schulthess GK, Steinert HC, Hany TF. Integrated PET/CT: current applications and future directions. Radiology. 2006;238(2):405-22.[4]Jones T. The role of positron emission tomography within the spectrum of medical imaging. Eur J Nucl Med. 1996;23(2):207-11.[5]Bruijnen STG, Verweij NJF, van Duivenvoorde LM, Bravenboer N, Baeten DLP, van Denderen CJ, et al. Bone formation in ankylosing spondylitis during anti-tumour necrosis factor therapy imaged by 18F-fluoride positron emission tomography. Rheumatology (Oxford). 2018;57(4):770.AcknowledgementsWe thank Pfizer and Novartis for financial support of this investigator initiated study.Disclosure of InterestsJerney de Jongh: None declared, Robert Hemke: None declared, Gerben C.J. Zwezerijnen: None declared, Maqsood Yaqub: None declared, Irene van der Horst-Bruinsma Speakers bureau: BMS, AbbVie, Pfizer, MSD, Consultant of: AbbVie, UCB, MSD, Novartis, Eli Lilly, Grant/research support from: Unrestricted Grants received for investigator initiated studies from MSD, Pfizer, AbbVie, UCB, Marleen G.H. van de Sande Speakers bureau: UCB, Consultant of: Advisory board AbbVie, Eli Lilly, Novartis, UCB, Grant/research support from: Novartis, Janssen, UCB, Eli Lilly, Arno Van Kuijk Speakers bureau: Novartis, Consultant of: Novartis, AbbVie, Janssen, Irene Bultink Speakers bureau: Eli Lilly, MSD, Amgen, UCB, GSK, Roche, Sanofi Genzyme (outsite the submitted work), Consultant of: Sanofi Genzyme, Astrazeneca (outside the submitted work), Lot Burgemeister Consultant of: Advisory board Novartis, Galapagos, Nancy M.A. van Dillen: None declared, Alexandre Voskuyl: None declared, Conny J. van der Laken: None declared