The performance of different
classification criteria sets for spondyloarthritis in
the ASAS-COMOSPA study

Background/Purpose: 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. However, the performance
of the different classification criteria sets has been insufficiently
evaluated. By this study we aim to compare the performance of different SpA classification criteria sets in the worldwide 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).

Conclusion: 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.