Background In 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.

Objectives To 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).

Methods All 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.

Results Of 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-CT

Conclusions This 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.

References

1. Devauchelle-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.

2. 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.

3. 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 radiological grading criteria for the diagnosis. Clin Rheumatol. 2012 Mar;31(3):425-8.

Disclosure of Interest None declared