Association between HLA-B27 and peripheral spondyloarthritis phenotype: results from the ASAS perSpA study.

OBJECTIVE: To analyse the influence of HLA-B27 in the phenotypical expression of peripheral spondyloarthritis (pSpA). METHOD: This is an observational cross-sectional study using data from the Assessment of SpondyloArthritis international Society perSpA registry, including all patients with an available HLA-B27 test result and with a diagnosis of pSpA or psoriatic arthritis (PsA) as per rheumatologist's judgement. Demographic and clinical data, presence of extra musculoskeletal manifestations (EMM) and fibromyalgia were the variables included in a simple and multiple logistic regression model to assess their association to HLA-B27 positivity. RESULTS: From the 4465 patients included in the registry, 790 were classified as having either pSpA or PsA and had the HLA-B27 typing available. HLA-B27-positive patients presented a male predominance, had an earlier disease onset and a shorter diagnostic delay compared with the negatives. HLA-B27-positive patients presented a higher frequency of axial involvement, radiographic sacroiliitis, enthesitis and uveitis. Also, root joint involvement, poliarticular joint patern and tarsitis were significantly higher within HLA-B27-positive patients. Furthermore, we did not observe any association between the presence of HLA-B27 and peripheral joint damage, dactylitis, other EMM (psoriasis, inflammatory bowel disease) or fibromyalgia.The multivariable analysis confirmed the independent association of HLA-B27 positivity with male sex, an earlier onset of the disease, the presence of axial involvement, tarsitis and uveitis. SUMMARY: In summary, the presence of HLA-B27 in pSpA patients was associated with earlier disease onset and higher axial involvement, tarsitis and uveitis, but not with other EMM, fibromyalgia or peripheral structural damage.