Background: Classification criteria for axial spondyloarthritis (axSpA) that capture the spectrum of disease present challenges due to the frequency of back pain, the relative infrequency of axSpA, and limited physical and laboratory findings in early disease. Several cohorts have reported the performance of the ASAS classification criteria in settings where patients have been selected for certain features such as the presence of inflammatory back pain and/or short symptom duration.

Objectives: We aimed to test the performance of the ASAS 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 and whether performance varied according to demographic factors and symptom severity.

Methods: he multicenter Screening for Axial Spondyloarthritis in Psoriasis, Iritis, and Colitis (SASPIC) Study is aimed at early detection of axial SpA. 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. Assessment of imaging was conducted by local and central readers. We calculated the sensitivity and specificity of the ASAS criteria and the component imaging and clinical arms using the stage 3 diagnostic assessment by the local rheumatologist as gold standard.

Results: 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 stage 3 evaluation. Sensitivity/specificity of the ASAS criteria, imaging arm, clinical arm were 74.4/79.8%, 55.6/93.8%, 50.4/82.2%, respectively (Table). For patients diagnosed with a high degree of confidence sensitivity/specificity was 87.5/82.7%, 68.8/94.5%, 56.3/84.5%, respectively. Specificity, especially for the clinical arm, was notably higher in patients with a higher degree of back pain (≥5/10), and in those with longer symptom duration (≥5 years).

Conclusion: The performance of the ASAS criteria in the SASPIC cohort is comparable to the findings in the original ASAS classification study. Performance may vary according to symptom duration and severity of symptoms which likely impacts diagnostic ascertainment. 

Disclosure of Interests: 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