Background/Purpose: To compare the respective performances of the pelvic plain radiograph (RX), thoraco-abdominal and pelvic CT (TAP-CT) and MRI of the sacroiliac joints (SIJ-MRI) to CT of the sacroiliac joints (SIJ-CT) for the diagnosis of structural sacroiliitis in a population suffering from spondyloarthritis (SpA) meeting the New York or ASAS criteria.

Methods: All radiographic or non-radiographic SpA patients eligible for biologic treatment who received a pretherapeutic check up including the four imaging techniques in the same year from 2005 to 2012 were selected. Sacroiliitis was assessed on Rx according to New York criteria independently by a rheumatologist and a radiologist and on TAP-CT, SIJ-MRI and SIJ-CT for the presence of erosion on at least two consecutive slices. A final diagnosis was established for conflicting exams.

Results: Of the 58 selected patients, sacroiliitis was diagnosed on RX, TAP-CT, SIJ-MRI and SIJ-CT in 32, 26, 34 and 35 times respectively. Inter-reader agreements were good for the grade of sacroiliitis (Kappas between 0.60 and 0.76) and moderate for the diagnosis of sacroiliitis (Kappas between 0.45 and 0.55) for the four imaging techniques. The sensitivities of RX, TAP-CT and SIJ-MRI in comparison to SIJ-CT were 82.8%, 71.4% and 85.7% respectively and the specificities were 86.9%, 100% and 82.6% respectively with SIJ-CT considered gold standard.

Conclusion: This study demonstrates the interest of SIJ-MRI and TAP-CT for the diagnosis of structural sacroiliitis in comparison with the SIJ-CT with the same level of performances as RX. These imaging techniques avoid redundant exams.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/pelvic-plain-radiograph-thoraco-abdominal-and-pelvic-ct-scan-and-mri-compared-to-the-ct-of-the-sacroiliac-joints-taken-as-gold-standard-in-the-diagnosis-of-structural-sacroiliitis/