Background/Purpose: Diagnosis and classification of axial spondyloarthritis (axSpA) relies considerably on imaging evidence of sacroiliitis which has led to the development of classification criteria which also rely on imaging. However, it has been suggested that such criteria may not be appropriate for axSpA patients presenting with other forms of SpA, especially psoriatic, because imaging features may vary in frequency and/or may be atypical. This hypothesis has never been tested in a prospective inception cohort of patients presenting with undiagnosed back pain. We aimed to compare the spectrum of radiographic and MRI abnormalities in the sacroiliac joint (SIJ) and spine of an inception cohort of patients presenting with undiagnosed back pain and psoriasis, iritis, and colitis.

Methods: We used data from the prospective multicenter Screening for Axial Spondyloarthritis in Psoriasis, Iritis, and Colitis (SASPIC) Study, which is aimed at early detection of axial SpA in patients referred by the respective specialist after first presenting with these disorders. Consecutive patients ≤45 years of age with ≥3 months undiagnosed back pain with any one of psoriasis, AAU, or colitis undergo routine clinical evaluation by a rheumatologist for axial SpA followed by imaging. In SASPIC I, MRI evaluation of the SIJ and whole spine was ordered per rheumatologist decision. In SASPIC II, MRI evaluation of the SIJ was ordered for all patients. Radiographs and MRI scans were assessed by two central readers and comparisons of the three groups were based on concordant assessments of imaging features. Evaluation of MRI scans included both global assessment for presence/absence of axSpA with confidence scale (-10 to +10), active and structural lesions typical of axSpA per recent ASAS definitions, and granular assessment of individual lesions according to SIJ quadrants and halves in consecutive semicoronal slices through the SIJ as well as detailed evaluation of active and structural lesions in individual discovertebral units of the spine on consecutive sagittal slices. Groups were compared by ANOVA and the chi-square test.

Results: A total of 240 patients were recruited, 143 from SASPIC I and 97 from SASPIC II, 101 (42.1%) being diagnosed with axSpA (65.3% male, mean age 34.4 years, mean symptom duration 8.7 years, B27 positive 55.4%). Mean age of colitis (N=101), psoriasis (N=61), iritis (N=78) patients were 33.4, 36.6, 34.3 years, respectively, mean symptom duration was 6.8, 7.2, 9.4 years, respectively, and % males were 45.5%, 52.5%, 51.3%, respectively. MRI scans of the SIJ were available in 101 patients and of these 41 also had MRI of the spine. There were no significant group differences for unilateral versus bilateral radiographic sacroiliitis and no significant differences in the frequencies, type, or distribution of MRI lesions in the SIJ and spine(Table). In particular, there was not a single case where there was an MRI indicative of axSpA in the spine that was not also evident in the SIJ.

Conclusion: Data from the SASPIC prospective inception cohort does not support the view that imaging of the SIJ and spine differs in psoriatic axSpA, which appears similar to axSpA associated with iritis or colitis. These data support the umbrella concept of axSpA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/does-imaging-of-the-sacroiliac-joint-and-spine-differ-in-patients-presenting-with-undiagnosed-back-pain-and-psoriasis-acute-anterior-uveitis-and-colitis-an-inception-cohort-study/