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Purpose To assess increased sacroiliac joint (SIJ) uptake on 18 F-NaF PET/CT and to compare with MRI for inflammation and with CT scan for structural damages in a population of 23 patients with spondyloarthritis (SpA). Methods Twenty-three patients with active SpA according to the Assessment of SpondyloArthritis international Society (ASAS) and/or modified NY criteria were included. All patients had a pelvic radiograph, MRI, and CT scan of the SIJ and 18 F-NaF PET/CT examinations within a month, analyzed by three blinded readers. MRIs were assessed according to the ASAS criteria and SPARCC method. On CT scans, erosion and ankylosis were quantified using the same methodology. On the 18 F-NaF PET, abnormal uptake was assessed using a qualitative method inspired by the ASAS criteria and two quantitative approaches (the PET-activity score according to the SPARCC method and Maximum Standardized Uptake Value (SUVmax)). Results Structural sacroiliitis was observed on 7 radiographs and 10 CT scans; 10 MRIs showed inflammatory sacroiliitis, and 20 patients had a positive PET. The inter-reader reliability was good for the PET activity score and good to excellent for the SUVmax. A positive PET was not correlated with a positive MRI or with a structural sacroiliitis on CT scan. The PET-activity score and SUVmax were correlated with the SPARCC inflammation score but not with erosion or ankylosis scores on CT scan. Conclusion Abnormal uptake by the SIJ on 18 F-NaF PET is more frequent than inflammatory and structural sacroiliitis in a population of SpA patients. The PET activity score and SUVmax had good correlations with inflammatory sacroiliitis but not with structural lesions on CT scan.

Background: The presence of structural sacroiliitis is strong evidence for the diagnosis of spondyloarthritis (SpA). Purpose: To assess the performance of abdominal computed tomography (CT) and pelvic plain radiography for the diagnosis of structural sacroiliitis compared with sacroiliac CT (SI joint CT) considered the reference technique in patients with SpA. Material and Methods: All SpA patients eligible for biologic treatment were selected from 2005 to 2012. An assessment of sacroiliitis was based on radiography according to the modified New York criteria and on abdominal CT and SI joint CT scans depending on the presence of erosion on at least two consecutive slices. A senior rheumatologist and radiologist independently scored the grade and diagnosis of structural sacroiliitis for the three imaging modalities. After a consensus reading of conflicting examinations (radiography and CT), a final diagnosis of structural sacroiliitis was attained. Results: Of the 72 patients selected, sacroiliitis was diagnosed on radiography, abdominal CT, and SI joint CT in 40, 31, and 44 patients, respectively. Inter-reader agreements for the grade of sacroiliitis were substantial for the three imaging modalities, with a weighted kappa range of 0.63-0.75 (95% confidence interval [CI], 0.52-0.83), and they were moderate for the diagnosis of sacroiliitis, with a kappa range of 0.50-0.55 (95% CI, 0.32-0.74). The sensitivity and specificity were 79.1% and 70.5%, respectively, for radiography and 82.1% and 100%, respectively, for abdominal CT. Conclusion: This study demonstrates the relevance of abdominal CT for the diagnosis of structural sacroiliitis, with good sensitivity and excellent specificity. These imaging techniques avoid unnecessary examinations.

BackgroundIn some countries, patients with spondyloarthritis are eligible to receive a TNF blocker only if they present with radiographic spondyloarthritis (AS). This study is therefore of interest with regard to validation of the use of other imaging modalities, particularly thoracic and pelvic CT scanning, to establish the diagnosis of structural sacroiliitis with the same level of performance as radiography.ObjectivesTo assess the performance of thoraco-abdominal and pelvic CT (TAP-CT) and pelvic plain radiography (RX) for the diagnosis of structural sacroiliitis compared to sacroiliac CT (SIJ-CT) in patients with spondyloarthritis (SpA).MethodsAll SpA patients eligible for biologic treatment with or without structural sacroiliitis on radiography (ASAS criteria) were selected from 2005 to 2012. The three imaging studies were performed in the same year. Sacroiliitis was assessed on RX according to New York criteria, and in TAP-CT and SIJ-CT scans depended on the presence of erosions on two consecutive slides. A senior rheumatologist and radiologist independently scored the grade and the diagnosis of structural sacroiliitis for the three imaging modalities. After a consensus reading of the conflicting exams (RX and CT), a final diagnosis of structural sacroiliitis was retained. The gold standard for the diagnosis of structural sacroiliitis was SIJ-CT.ResultsOf the 72 patients selected, sacroiliitis was diagnosed on RX, TAP-CT and SIJ-CT in 40, 31 and 44 respectively. Inter-reader agreements for the grade of sacroiliitis were good for the three imaging modalities with a weighted kappa that varied between 0.63 and 0.75 (IC-95%: 0.52-0.83). Inter-reader agreements for the diagnosis of sacroiliitis were moderate with a kappa that varied between 0.50 and 0.55 (CI-95%: 0.32-0.74). For the RX and the TAP-CT, the sensitivity and the specificity were respectively 79.1%, 70.5%, and 82.1%, 100%. Finally, 4 out of 5 patients were correctly classified on RX or TAP-CTConclusionsThis study demonstrates the interest of TAP-CT for the diagnosis of structural sacroiliitis with a good sensitivity and an excellent specificity. This imaging technique systematically performed in various clinical situations would limit the prescription of additional exams to establish the diagnosis of structural sacroiliitis.ReferencesDevauchelle-Pensec V, D'Agostino MA, Marion J, Lapierre M, Jousse-Joulin S, Colin D et al. Computed tomography scanning facilitates the diagnosis of sacroiliitis in patients with suspected spondylarthritis: results of a prospective multicenter French cohort study. Arthritis Rheum. 2012 May; 64(5):1412-9.Geijer M, Göthlin GG, Göthlin JH. The clinical utility of computed tomography compared to conventional radiography in diagnosing sacroiliitis. A retrospective study on 910 patients and literature review. J Rheumatol. 2007 Jul; 34(7):1561-5.Slobodin G, Croitoru S, Starikov N, Younis S, Boulman N, Rimar D et al. Incidental computed tomography sacroiliitis: clinical significance and inappropriateness of the New York radiologi...

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