THU0361 DIAGNOSTIC PERFORMANCE OF MRI LESIONS IN THE SACROILIAC JOINTS ACCORDING TO UPDATED ASAS LESION DEFINITIONS: A CENTRAL READER ASSESSMENT OF MRI SCANS FROM THE ASSESSMENTS IN SPONDYLOARTHRITIS CLASSIFICATION COHORT
Authors: Walter P Maksymowych, Robert G Lambert, Xenofon Baraliakos, Susanne Juhl Pedersen, Pedro Machado, Joachim Sieper, Stephanie Wichuk, Denis Poddubnyy, Joel Paschke, Mikkel Ǿstergaard, Ulrich Weber
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background:</h3> The ASAS MRI group has generated updated lesion definitions for MRI lesions in the SIJ. While the ASAS definition of a positive MRI for classification purposes remains unchanged, these additional ASAS definitions for active and structural lesions may also be of diagnostic value. It is important to understand their relative contribution and complementarity as diagnostic indicators. <h3>Objectives:</h3> To determine optimal cut-offs for the number of SIJ quadrants with MRI lesions reflecting diagnosis of axSpA in patients with undiagnosed back pain. <h3>Methods:</h3> MRI lesions on baseline scans from the ASAS Classification Cohort were recorded by 7 experienced readers from the ASAS-MRI group. Detailed scoring of lesions per SIJ quadrant (SPARCC SIJ quadrantic method) was available for assessment of bone marrow edema (BME) and structural lesions in 158 and 146 cases, respectively, who were diagnosed by the local rheumatologist at baseline. Of these, 86 and 79 cases with BME and structural lesion data, respectively, were also diagnosed by the local rheumatologist at follow up (mean 4.4 years). We calculated sensitivity and specificity for varying numbers of SIJ quadrants with MRI lesions with rheumatologist diagnosis of axSpA at baseline and follow up as gold standard. <h3>Results:</h3> Lesion cut-offs based on BME were most sensitive for diagnosis at baseline and follow up but erosion- and fatty-lesion cut-offs were more specific (Table). At least 2 SIJ quadrants with erosion or fat metaplasia were associated with &gt;90% specificity for the diagnosis of axSpA. There was also a consistent improvement in the sensitivity and specificity performance of cut-offs based on erosions and fatty lesions according to diagnosis at baseline and at follow up after 4.4 years but not for cut-offs based on BME. Lesion cut-offs that combined BME and/or erosion enhanced sensitivity without compromising specificity. <h3>Conclusion:</h3> The updated ASAS definitions based on the presence of MRI lesions in 2-3 SIJ quadrants have comparable diagnostic performance. This performance improves for erosion and fatty lesion cut-offs after follow up. <h3>Disclosure of Interests:</h3> Walter P Maksymowych Grant/research support from: AbbVie, Pfizer, Janssen, Novartis, Consultant for: AbbVie, Eli Lilly, Boehringer, Galapagos, Janssen, Novartis, Pfizer and UCB Pharma; Chief Medical Officer for Canadian Research and Education Arthritis, Robert G Lambert Consultant for: Bioclinica, Parexel, Abbvie, Xenofon Baraliakos Grant/research support from: AbbVie, Boehringer Ingelheim, Bristol-Myers Squibb, Celgene, Centocor, Chugai, Janssen, MSD, Novartis, Pfizer Inc, Roche and UCB, Grant/research support from: AbbVie, Pfizer, Merck Sharp &amp; Dohme, UCB Pharma, Novartis, Consultant for: AbbVie, Bristol-Myers Squibb, Boehringer Ingelheim, Celgene, Chugai, Janssen Biologics, Novartis, Pfizer, UCB Pharma, Galapagos, Speakers bureau: AbbVie, Chugai, Janssen, Novartis, Pfizer, UCB Pharma, Susanne Juhl Pedersen: None declared, Pedro Machado Consultant for: Abbvie, BMS, Celgene, Janssen, MSD, Novartis, Pfizer, Roche and UCB, Speakers bureau: Abbvie, BMS, Celgene, Janssen, MSD, Novartis, Pfizer, Roche and UCB, Joachim Sieper Consultant for: Abbvie, Böhringer Ingelheim, Janssen, Lilly, Merck, Mylan, Novartis, Pfizer, UCB., Speakers bureau: Abbvie, Böhringer Ingelheim, Janssen, Lilly, Merck, Mylan, Novartis, Pfizer, UCB., Stephanie Wichuk: None declared, Denis Poddubnyy Grant/research support from: AbbVie, Merck Sharp &amp; Dohme, Novartis, Consultant for: AbbVie, Bristol-Myers Squibb, Janssen, Merck Sharp &amp; Dohme, Novartis, Pfizer, UCB Pharma, Speakers bureau: AbbVie, Bristol-Myers Squibb, Janssen, Merck Sharp &amp; Dohme, Novartis, Pfizer, Roche, UCB Pharma, Joel Paschke: None declared, Mikkel Ǿstergaard Grant/research support from: Abbvie, Celgene, Centocor, Merck, Novartis, Consultant for: Abbvie, BMS, Boehringer-Ingelheim, Celgene, Eli Lilly, Hospira, Janssen, Merck, Novartis, Novo, Orion, Pfizer, Regeneron, Roche, and UCB, Speakers bureau: Abbvie, BMS, Boehringer-Ingelheim, Celgene, Eli Lilly, Hospira, Janssen, Merck, Novartis, Novo, Orion, Pfizer, Regeneron, Roche, and UCB, Ulrich Weber Consultant for: Abbvie&nbsp;