Background CBP is nowadays the starting point for the ASAS classification criteria for axSpA. Later, two possible entry criteria based on complementary examinations (HLA-B27 and imaging) are considered. However, CBP is a very prevalent symptom so it is necessary to identify those characteristics more likely resulting in a positive complementary test.
Objectives To evaluate which inflammatory characteristics of CBP are associated with the presence of HLA-B27 in patients with suspected axSpA.
Methods Baseline dataset from the EsPeranza cohort (<45 yrs, symptoms duration 3-24 months and with inflammatory back pain -IBP- or asymmetrical arthritis or spinal/joint pain plus ≥1 SpA features) was used. Data from 653 patients with axial symptoms and HLA-B27 assessed were analysed. Odds ratio were estimated for the association between IBP characteristics (morning stiffness, improve with exercise and not with rest, alternating buttock pain, insidious onset, awakening at 2nd half of night and good response to NSAIDs) and their different combinations with a positive HLA-B27 (local lab test).
Results A total of 270 (41%) patients were HLA-B27+. Table shows results for the association between individual and combined IBP characteristics with HLA-B27+. Awakening at 2nd half of night (OR=1.53;p<0.05) and response to NSAID (OR=1.46; p<0.05) were the only characteristics independently associated with HLA-B27+ but had lower specificity than the existing criteria combining several characteristics. The addition of these two characteristics to these criteria just improved their specificity slightly. Among the existing criteria to define IBP, the ASAS criteria were the most strongly associated with HLA-B27 and the most specific.
Conclusions Awakening at second half of night and good response to NSAIDs are both related to positive HLA-B27 in patients with suspected axSpA although they are less specific than the existing criteria to define IBP. The most specific criteria for a positive HLA-B27 are the ASAS criteria.
Acknowledgements The EsPeranza Program has been supported by an unrestricted grant from Pfizer
Disclosure of Interest None declared