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Background:Dual energy computed tomography (DECT) is highly accurate for the diagnosis of gout. However, many artifacts have been described (1,2) such as nail bed, skin, beam hardening, sub-millimeter and vascular artifacts). Their presence can lead to a risk of over-diagnosis (false positives).Objectives:Main objective of this case-control study was to determine the optimal DECT settings post-treatment parameters (ratio and attenuation coefficient (HU)) in order to reduce the frequency of lower limb artifacts in patients with suspected gout of the lower limbs.Methods:Seventy-seven patients hospitalized for suspected gout arthritis (feet/ankles and/or knees) who received a DECT imaging were consecutively included (final diagnosis of 43 gout and 34 other rheumatic disorders). Different post-treatment settings were evaluated from the Syngovia software: an R1 (standard) setting with a ratio at 1.36 and minimum attenuation at 150 HU; an R2 setting with a ratio at 1.28 and minimum attenuation at 170 HU and an R3 setting with a ratio at 1.28 and minimum attenuation at 120 HU. The frequency of each artifact according to the 3 settings was determined. Diagnostic accuracy of R1 and R2 settings has been calculated. Correlations between artefacts and patient’s clinical characteristics were obtained by performing a Spearman test.Results:The R2 setting (170 HU, ratio=1.28) significantly reduced the presence of knee and foot/ankle artifacts compared to the standard R1 setting (85% and 94% decrease in beam hardening and clumpy artifacts in the ankle and foot, respectively (p < 0.001); a decrease of 71%, 60% and 88% respectively of meniscal beam hardening, beam hardening and submillimeter artifacts in the knee (p < 0.001). The use of R3 setting lead to a significant increase of some artifacts (clumpy artifacts, skin artifacts, beam hardening and nail beds.). In addition, our results found a positive correlation between the presence of deposits of knee menisci beam hardening chondrocalcinosis. Body mass index was also positively correlated with the presence of knee beam hardening artifact. Compared to standard setting, the use of R2 settings decreased sensitivity (0.79 [95CI: 0.65;0.88] versus 0.90 [95CI: 0.78;0.96] and increased specificity (0.86 [95CI: 0.71;0.93) versus 0.63 [95CI: 0.47;0.77] (pConclusion:Applying a ratio of 1.28 and a minimum attenuation of 170 HU (R2 settings) in DECT post-processing eliminates the majority of the artifacts located on the lower limbs, particularly the clumpy artifact and the beam hardening artifact.References:[1]Neogi T, Jansen TLTA, Dalbeth N, Fransen J, Schumacher HR, Berendsen D, et al. 2015 Gout classification criteria: an American College of Rheumatology/European League Against Rheumatism collaborative initiative. Ann Rheum Dis. 2015;74:1789-98.[2]Mallinson PI, Coupal T, Reisinger C, Chou H, Munk PL, Nicolaou S, et al. Artifacts in dual-energy CT gout protocol: a review of 50 suspected cases with an artifact identification guide. AJR 2014;203:W103-109.Disclosure of Interests:None declared.

Background:In routine practice, axial spondyloarthritis (SpA) can be a diagnostic challenge because there is potential overlap with osteoarthritic low back pain or diffuse polyalgic syndrome with axial pain as fibromyalgia. Internationally recognized classification criteria (AMOR, ASAS (1), ESSG (2)) are often used as diagnostic tools in clinical practice (3), but few studies have sought to establish their “real life” diagnostic performances.Objectives:This monocentric study aimed to evaluate the diagnostic performance of different sets of classification criteria for SpA in patients with chronic back pain hospitalized for suspected axial SpA. The second objective was to evaluate the impact of the sacroiliac MRI reading according to the ASAS MRI reading or expert musculoskeletal reading.Methods:Patients presenting with inflammatory low back pain who underwent standardized sacroiliac MRI protocol were consecutively included. The diagnoses obtained with the classification criteria (AMOR, ESSG, Modified AMOR and Modified ESSG (with sacroiliac MRI)) were compared to the gold standard diagnoses (made by a college of three experienced rheumatologists). Two readings of the sacroiliac MRI were performed (ASAS MRI reading and Expert MRI reading (including all inflammatory or structural T1 or T2 STIR abnormalities)). Diagnostic performance was measured for each set of classification criteria: sensitivity, specificity, predictive positive and negative values (PPV, NPV) and positive and negative likelihood ratios (PLR, PLN). The clinical, biological and MRI factors associated with axial SpA diagnosis were identified in a multivariate logistic regression model.Results:83 patients were included of which 27 had axial SpA according to the opinion of the college of rheumatologists. The AMOR modified criteria (with ASAS MRI reading) had the highest diagnostic performance values, with sensitivity = 96%, specificity = 71%, NPV = 97%, PPV = 54%, PLR = 3.3, and NLR = 0.06. Sacroiliac MRI reading demonstrated poor sensitivity (< 60%) for SpA (ASAS or expert reading), while expert reading of MRI had high specificity (98%), NPV = 90%, PPV = 78%, and PLR = 18. In multivariate logistic regression, the presence of enthesitis (OR = 3.51, IC95% [1.10;11.21]; p = 0.024), positive HLA B27 (OR = 4.22, IC95% [1.25;14.18]; p = 0.02)) or sacroiliitis on MRI (ASAS reading) (OR = 3.34, IC95% [1.04; 10.76]; p = 0.043) were independently associated with the final diagnosis of SpA.Conclusion:The results of this pragmatic study suggest that the Modified AMOR criteria with ASAS MRI reading can be used to rule out axial spondyloarthritis (NPV = 97%). However, the use of an MRI ASAS reading alone creates a risk of false positives because of the greater impact on ASAS criteria compared to AMOR or ESSG criteria. Further international studies are needed to decrease the rate of false positives in suspected cases of axial spondyloarthritis in routine practice.References:[1]Dougados M, van der Linden S, Juhlin R et al. The European Spondylarthropathy Study Group preliminary criteria for the classification of spondylarthropathy. Arthritis Rheum 1991;34:1218-27.[2]Rudwaleit M, van der Heijde D, Landewé R et al. The development of Assessment of SpondyloArthritis international Society classification criteria for axial spondyloarthritis (part II): validation and final selection. Ann Rheum Dis. 2009;68:777-83.[3]Gazeau P, Cornec D, Timsit MA et al. Classification criteria versus physician’s opinion for considering a patient with inflammatory back pain as suffering from spondyloarthritis. Joint Bone Spine 2018;85:85-91.Disclosure of Interests:None declared

Background:The gold-standard for diagnosis of gout is the identification of monosodium urate (MSU) crystal in joint fluid. However, the sensitivity, specificity, and reproducibility of such analysis are not excellent, and joint aspiration is sometimes difficult, or impossible. The Nijmengen score is an easy-to-use rule without joint fluid analysis with excellent validity, in primary as well as in secondary care (1, 2). However, it’s validity as not been evaluated in the particular situation of patients whose acute arthritis necessitates hospitalization.Objectives:The objective of the present study was to assess diagnosis performances of the score in patients hospitalized for acute monoarthritis.Methods:Inclusion: all patients hospitalized for acute monoarthritis in the rheumatology department of the Dijon University Hospital between 2016 and 2019.Assessment: 1- clinical examination by an experimented rheumatologist; 2- joint aspiration and synovial fluid analysis following aspiration; 3- ultrasound (US) examination of the knees, first metatarso-phalangeal joints, and arthritic joint by a trained rheumatologist; 4- dual-energy computed tomography (DECT) of the arthritic joint; 5- Nijmengen score (cutoff scores of ≥ 8 needed for diagnosis of gout, and ≤ 4 to rule out gout) and ACR/EULAR 2015 classification criteria (3) (cut-off score of ≥ 8 needed for diagnosis of gout).Analysis: positive and negative predictive values, and ROC curve analysis of the Nijmengen score, using as gold-standard on one hand the results of the MSU crystal research, on the other hand those of the ACR/EULAR criteria.Results:A total of 39 patients were included (mean age = 69.8 ± 15 years, 74.4 % males, mean BMI = 27.5 ± 4.6 Kg/m2, mean serum uric acid = 354.6 ± 117.5 µmol/l). The affected joints were the knee (n = 31), ankle (n = 3), hip (n = 2), wrist (n = 2), shoulder (n = 1). Joint fluid analysis revealed MSU crystal in 11 patients. The ACR/EULAR was ≥ 8 in 15 patients. The Nijmengen score was ≥ 8 in 11 patients, including 5 with MSU crystal on joint fluid analysis and 9 with an ACR/EULAR score ≥ 8. The Nijmengen score was ≤ 4 in 15 patients, including 14 with no MSU crystal on joint fluid analysis and 14 with an ACR/EULAR score < 8. The positive predictive values of a Nijmengen score ≥ 8 were 45 % (joint fluid analysis as gold standard) and 81.8 % (ACR/EULAR). The negative predictive values of a Nijmengen score ≤ 4 were 93.3 % (joint fluid analysis and ACR/EULAR as gold standard). On ROC curve analyses, the areas under the curve were 0.763 (95% CI = 0.612 – 0.914) using joint fluid analysis as gold standard (figure 1) and 0.908 (95% CI = 0.814 – 1.0) using the ACR/EULAR score as gold standard (figure 2).Fig. 1ROC curve (fluid analysis as gold standard)Fig. 2Roc curve (ACR/EULAR as gold standard)Conclusion:Although having been developed for use in primary-care, the Nijmengen score appears to be useful in patients hospitalized for acute monoarthritis in a rheumatology unit.References:[1]Janssens et al. A diagnostic rule for acute gouty arthritis in primary care without joint fluid analysis. Arch Intern Med 2010; 170:1120-6.[2]Kienhorst L et al. The validation of a diagnostic rule for gout without joint fluid analysis: a prospective study. Rheumatology 2015; 54:609-14.[3]Neogi T et al. 2015 Gout Classification Criteria: An American College of Rheumatology/European League Against Rheumatism Collaborative Initiative: ACR/EULAR CLASSIFICATION CRITERIA FOR GOUT. Arthritis and Rheumatology. oct 2015;67(10):2557-68.Disclosure of Interests: :marie Schmitt: None declared, André Ramon: None declared, Paul Ornetti: None declared, jean Francis Maillefert Grant/research support from: Abbot, shugai, Roche, pfiser, BMS,, Speakers bureau: Abbot, Shugai, Roche, Pfiser, BMS

Background:The reasons explaining why some patients exhibit higher monosodium urate (MSU) crystal burdens than others remain largely unknown. While MSU crystal formation is enhanced by certain factors in vitro such as pH, temperature, and other ion concentrations, it is currently unknown whether comorbidities and clinical features are associated with increased MSU deposition in vivo.Objectives:To determine which factors are associated with the burden of MSU crystal deposition quantified by dual-energy CT (DECT) in urate lowering therapy (ULT)-naive gout patients.Methods:In this multicenter cross-sectional study, DECT scans of knees and feet were prospectively obtained from ULT-naive, or not taking any ULT for more than a year, gout patients. Demographic, clinical (including gout history and comorbidities), and biological data were collected, and their association with DECT MSU crystal volume was analyzed using bivariate and multivariate analyses. A second bivariate analysis was performed by splitting the dataset depending on an arbitrary threshold of DECT MSU volume (1 cm3).Results:A total of 125 gout patients were included, of whom 91 underwent both DECT scans of knees and feet. In bivariate analysis, age (p=0.03), symptom duration (p=0.003), subcutaneous tophi (p=0.004), hypertension (p=0.02), diabetes mellitus (p=0.05), and chronic heart failure (p=0.03) were associated with the total DECT volume of MSU crystal deposition. In multivariate analysis, factors associated with DECT MSU volumes ≥1 cm3 were gout duration (OR for each 10-year increase 3.15 [1.60;7.63]), diabetes mellitus (OR 4.75 [1.58;15.63]), and chronic heart failure (OR 7.82 [2.29;31.38]). The model performance was good with an AUC of 0.816.Conclusion:Specific comorbidities, particularly chronic heart failure, diabetes mellitus, and hypertension, are more strongly associated with increased MSU crystal deposition in knees and feet than gout duration, regardless of serum urate level.Disclosure of Interests: :Tristan Pascart Grant/research support from: Research Grant Horizon Pharma, Consultant of: Novartis, BMS, Sanofi, Pfizer,, Speakers bureau: Novartis, BMS, André Ramon: None declared, Sebastien Ottaviani: None declared, Julie Legrand: None declared, Vincent Ducoulombier: None declared, Eric Houvenagel Speakers bureau: Janssen, Novartis, Laurène Norberciak: None declared, Pascal Richette: None declared, Fabio Becce: None declared, Paul Ornetti: None declared, Jean-François Budzik: None declared