Background Spondyloarthritis (SpA) includes patients with (predominantly) axial spondyloarthritis (axSpA) and patients with (predominantly) peripheral spondyloarthritis (pSpA) including psoriatic arthritis (PsA). Over time, several classification criteria sets have been developed to cover the whole spectrum of SpA.
Objectives To compare the performance of different SpA classification criteria sets in the ASAS-COMOSPA study.
Methods The ASAS-COMOSPA study is an international, cross-sectional study. Patients clinically diagnosed with SpA by the rheumatologist were included consecutively via routine care. For this analysis, patients were classified according to the ESSG, AMOR, mESSG (addition of MRI), mAMOR (addition of MRI), CASPAR and ASAS criteria for axSpA and pSpA.
Results From 5 continents, 22 participating countries included 3984 patients: age 44±14 years, 65% male gender, 56.2% HLA-B27+, psoriasis: 21.4%, uveitis: 19.6%, peripheral arthritis: 61.5%, mNY+ 64.4%, sacroiliitis on MRI (ASAS definition): 33.6%, negative rheumatoid factor (RF): 80.6%. Patients with up to 6 missing values were included (missing values set as absent); patients with ≥7 variables missing were left out of the analysis. Most common missing variables: MRI of the sacroiliac joints (ASAS definition; MRI-SI) (n=1951), juxta-articular bone formation (n=999), HLA-B27 (n=907), good response to NSAIDs (n=803), RF (n=613), radiographic sacroiliitis (n=341). Patients were classified according to the different classification criteria sets (table): data shown for all patients (left) and for patients with complete data regarding presence/absence of (radiographic/MRI) sacroiliitis and HLA-B27 (right). In addition, the overlap between the different classification criteria sets was assessed for patients with back pain and patients without back pain. The majority (of the patients) was classified by AMOR & ESSG & ASAS axSpA-criteria (n=1068). Most of the patients that were picked up by 1 criteria set only were classified by the ASAS axSpA-criteria (n=141; n=27 by AMOR and n=25 by ESSG). Similar trends were seen with regard to the mESSG and mAMOR-criteria. Regarding the patients with no back pain (peripheral complaints): again substantial overlap between the criteria was seen (ASAS pSpA, AMOR, ESSG, CASPAR. Patients fulfilling the imaging arm of the ASAS axSpA-criteria did not differ from patients fulfilling the clinical arm regarding the presence of most of the SpA-features. However, there were some notable differences: male gender (57.1% versus 62.8%), uveitis (13.3% versus 29.9%) and elevated CRP (52.0% versus 42.7%), imaging resp. clinical arm.
Conclusions In this worldwide ASAS-COMOSPA study including established patients with SpA according to the rheumatologist, most patients fulfil several classification criteria sets; the biggest overlap between AMOR, ESSG and ASAS SpA. If patients fulfil only 1 criteria set this is most frequently the ASAS axSpA-criteria. Patients fulfilling the imaging arm or the clinical arm are comparable regarding most disease characteristics.
Acknowledgements Study was conducted under the umbrella of ASAS and financially supported by unrestricted grants from Abbvie, Pfizer and UCB.
Disclosure of Interest None declared