AB0726 WHAT IS THE IMPACT OF MRI ON THE PERFORMANCE OF THE ASAS CLASSIFICATION CRITERIA IN PATIENTS PRESENTING WITH UNDIAGNOSED BACK PAIN?
Authors: Walter P. Maksymowych, Raj Carmona, James Yeung, Jon Chan, Liam Martin, Sibel Aydin, Dianne Mosher, Ariel Masetto, Stephanie Keeling, Olga Ziouzina, Sherry Rohekar, Joel Paschke, Amanda Carapellucci, Robert G. Lambert
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background:</h3> Several cohorts have reported the performance of the aSAS classification criteria in settings where clinical, radiographic, and MRI features have been simultaneously incorporated into the diagnostic evaluation in arriving at a gold standard for the testing of the criteria. MRI improves diagnostic precision but access is limited and it is therefore still important to understand how the criteria perform in a setting where diagnostic evaluation can be conducted sequentially before and after MRI assessment. We hypothesized that the aSAS criteria would demonstrate enhanced specificity when MRI is available due to enhanced diagnostic precision. <h3>Objectives:</h3> We aimed to test the impact of adding MRI to the diagnostic evaluation on the performance of the classification criteria in unselected patients referred with undiagnosed back pain who have presented with acute anterior uveitis (AAU), psoriasis, or colitis to their respective specialists. <h3>Methods:</h3> Consecutive patients ≤45 years of age with ≥3 months undiagnosed back pain with any one of psoriasis, acute anterior uveitis (AAU), or colitis undergo routine clinical evaluation by a rheumatologist for axial SpA and MRI evaluation is ordered per rheumatologist decision. The rheumatologist determines the presence or absence of axial SpA and the degree of confidence in the diagnosis (-10 (definitely not SpA) to +10 (definite SpA)) at 3 consecutive stages: 1. After the clinical evaluation; 2. After the results of labs (B27, CRP) and radiography; 3. After the results of MRI evaluation. We calculated the sensitivity and specificity of the aSAS criteria and the component imaging and clinical arms using the stage 2 and 3 diagnostic assessments by the local rheumatologist as gold standard. <h3>Results:</h3> A total of 246 patients were recruited, 47.6% being diagnosed with axSpA (61.5% male, age 33.7 years, symptom duration 7.6 years, B27 positive 52.1%), after final diagnostic evaluation. Sensitivity/specificity of the aSAS criteria, imaging arm, clinical arm after stage 2 diagnostic evaluation for the entire cohort were 67.4/85.7%, 39.7/95.2%, 48.9/87.6%, respectively (Table). For the subset of 146 patients who had MRI and had diagnostic evaluation at both stage 2 (pre-MRI) and stage 3 (post-MRI), sensitivity of the criteria was greater but specificity was lower when tested against the stage 3 diagnosis. This was particularly apparent in the clinical arm. <h3>Conclusion:</h3> The aSAS criteria were less specific when MRI assessment was added to the process of diagnostic evaluation, which could reflect rheumatologist over-interpretation of both clinical and radiographic findings in this population with higher pre-test probability of axSpA. <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, Raj Carmona Grant/research support from: amgen, abbvie, Jannsen, Consultant for: amgen, abbvie, BMS, Eli Lilly, Merck, Novartis, Jannsen, Takeda, UCB, James Yeung: None declared, Jon Chan Grant/research support from: Janssen, UCB, Novartis, Pfizer, Celgene, Consultant for: amgen, Celgene, Eli Lilly, Janssen, amgen, abbvie, Novartis, Pfizer, UCB, Sandoz, Merck, Liam Martin: None declared, Sibel aydin Consultant for: abbvie, Celgene, UCB, Novartis, Jannsen, Sanofi, Dianne Mosher: None declared, ariel Masetto Grant/research support from: amgen, Sanofi, Consultant for: Sanofi, Pfizer, Bristol-Myers Squibb, Novartis, Boehringer ingelheim, Speakers bureau: Novartis, Stephanie Keeling Consultant for: abbVie. Pfizer, Eli Lily, Janssen, amgen, astrzeeneca, UCB., Olga Ziouzina: None declared, Sherry Rohekar Consultant for: abbvie, amgen, BMS, Celgene, Eli-Lilly, Janssen, Merck, Novartis, Pfizer, Roche, Sanofi, UCB, Joel Paschke: None declared, amanda Carapellucci: None declared, Robert G Lambert Consultant for: Bioclinica, Parexel, abbvie