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Table 2. Number and proportion of patients meeting the different criteria sets. The classification rate was defined as the proportion of patients fulfilling a particular classification criteria set.
Criteria set N=581 (%)
ASAS SpA criteria 468 80.6 ASAS axial SpA 252 43.4 Imaging arm 198 34.1 Clinical arm 54 9.3 ASAS peripheral SpA 216 37.2 ESSG criteria 431 74.1 ESSG with MRI pos included* 438 75.4 Amor criteria 309 53.1 Amor with MRI pos included* 335 57.7
CI (95%)
77.1 – 84.7 39.3 – 47.5
33.2 – 41.3 70.4 - 77.7 71.7 – 78.9 49.0 – 57.3 53.5 – 61.7
*Inclusion of MRI as a surrogate for radiographic damage of sacroiliitis (active inflammatory changes) into the original criteria. ESSG, European Spondylarthropathy Study Group; ASAS, Assessment of Spondyloarthritis international Society; MRI, magnetic resonance imaging.
Table 3. Concordance among the different classification criteria sets. ESSG
Criteria ASAS SpA ESSG +MRI Amor ESSG 71.3 - - -
ESSG + MRI* Amor
Amor + MRI*
72.5 98.5 - - 57.1 70.4 69.2 - 60.9 72.2 72.6 95.5
*Inclusion of MRI as a surrogate for radiographic damage of sacroiliitis (active inflammatory changes) into the original criteria. ESSG, European Spondylarthropathy Study Group; ASAS, Assessment of Spondyloarthritis international Society; MRI, magnetic resonance imaging.
No single SpA feature explained differences in the fulfilment of classification criteria. Chronic back pain, IBP, enthesitis and alternating buttock pain were significantly more common in those patients meeting all three criteria sets compared with those who did not meet any of the criteria, nevertheless these features were frequently present in both groups (table-4). Interestingly, in the group of patients who fulfilled ESSG or Amor but not the ASAS-criteria, HLA-B27 positivity was
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