BackgroundImaging role in large vessel vasculitis (LVV) patients is tremendously increased in recent years. However, the role of 18F-FDG PET in evaluating treatment response is still an unmet need.ObjectivesThe aim of the present study is to evaluate the effect of different treatment regimens, namely glucocorticoids (GC), conventional disease modifying anti-rheumatic drugs (cDMARDs) and tocilizumab (TCZ), on clinical and metabolic activity of giant cell arteritis (GCA) with extra-cranial involvement.MethodsConsecutive LVV inpatients and outpatients, classified as GCA, were prospectively enrolled. We included all patients who underwent to at least 2 consecutive 18F-FDG PET-CT or MR scan between October 2010 and October 2021. Demographic and clinical data as well as disease activity were assessed before every PET scan. Remission was defined absence of signs and symptoms attributable to GCA and normalization of ESR (<30 mm/Hr) and CRP (<1 mg/dL) [1].GCA patients were compared according to current treatment regimen: GC monotherapy versus cDMARDs (methotrexate, azathiopirine) and versus TCZ (administered both subcutaneous and intravenous). For each PET scan the vessel’s metabolic activity was evaluated using the Meller’s grading [2] and the PETVAS score [3].ResultsThe study included 47 patients (age 66 [60-70], 72.3% female) exposed to a total of 77 treatment regimens (n=37 GC monotherapy, n=26 cDMARDs, n=14 TCZ). A total of 181 PET scan were conducted (min 2 – max 6). Overall clinical remission rate during the follow-up was 75.7% in GC-treated patients, 69.2% in cDMARDs-treated and 85.7% in TCZ-treated (p=0.513).Persistence was comparable among the different treatment regimens (GC 19±10 months vs cDMARDs 22±16 months vs TCZ 23±11 months, p=0.445).All the treatment led to significant reduction of acute phase reactants (GC-treated: ESR 50vs20 mmh, p<0.001, ΔESR= -43.3%, CRP 13.6vs5.3 mg/L, p=0.001, ΔCRP= -87.7%; cDMARDs-treated: ESR 36vs27 mmh, p=0.134, ΔESR= -152%, CRP 13.6vs5.3 mg/L, p=0.038, ΔCRP= -66.3% and TCZ-treated: ESR 27vs3 mmh, p=0.017, ΔESR= -86.7%, CRP 11.4vs2.7 mg/L, p=0.023, ΔCRP= -80.2%).Significant improvement in PETVAS was observed only in TCZ-treated patients (12vs4, p=0.002, ΔPETVAS -66.7%), while the other treatment approaches resulted not significant (GC treated 12vs5, p=0.052, ΔPETVAS= -50%; cDMARDs 11vs4, p=0.124, ΔPETVAS -52.4%).Daily prednisone dose at last examination was 4.5 [0-5] mg/d in the cDMARDs group vs 1.25 [0-5] mg/d in the TCZ group (p=0.057). Interestingly, at last PET examination low-grade inflammation (Meller 1-2) was observed in 56.8% of GC-treated patients, 57.7% of cDMARDs-treated patients and 64.3% of TCZ-treated patients (p=0.884).Conclusion18F-FDG PET may be useful in assessing disease activity and monitoring response to therapy. Tocilizumab treatment significantly reduce vessel’s metabolic activity over time, when compared to conventional treatment. A persistent low-grade uptake during remission is common features in LVV patients, irrespectively of treatment regimens.References[1]Stone JH, Tuckwell K, Dimonaco S, Klearman M, Aringer M, Blockmans D, Brouwer E, Cid MC, Dasgupta B, Rech J, Salvarani C, Schett G, Schulze-Koops H, Spiera R, Unizony SH, Collinson N. Trial of Tocilizumab in Giant-Cell Arteritis. N Engl J Med. 2017 Jul 27;377(4):317-328. doi: 10.1056/NEJMoa1613849. PMID: 28745999.[2]Meller J, Grabbe E, Becker W, Vosshenrich R. Value of F-18 FDG hybrid camera PET and MRI in early takayasu aortitis. Eur Radiol. 2003 Feb;13(2):400-5. doi: 10.1007/s00330-002-1518-8. Epub 2002 Jun 29. PMID: 12599007.[3]Grayson PC, Alehashemi S, Bagheri AA, Civelek AC, Cupps TR, Kaplan MJ, Malayeri AA, Merkel PA, Novakovich E, Bluemke DA, Ahlman MA. 18 F-Fluorodeoxyglucose-Positron Emission Tomography As an Imaging Biomarker in a Prospective, Longitudinal Cohort of Patients With Large Vessel Vasculitis. Arthritis Rheumatol. 2018 Mar;70(3):439-449. doi: 10.1002/art.40379. Epub 2018 Feb 6. PMID: 29145713; PMCID: PMC5882488Figure 1.Disclosure of InterestsNone declared