Axial involvement according to ASAS criteria in an observational psoriatic arthritis cohort

The definition of axial involvement in psoriatic arthritis (PsA) is still under debate. Currently, the axial spondyloarthritis (SpA) criteria defined by Assessment of Spondyloarthritis International Society (ASAS) may be the most adequate.(1) The aims of present study were to assess axial involvement according to ASAS criteria in an observational PsA cohort and define the clinical characteristics more associated with this kind of involvement. Our study included consecutive patients who had a visit in a tertiary Rheumatology centre. All patients included fulfill ClASsification criteria for Psoriatic Arthritis (CASPAR) criteria for PsA and all of them had a recent radiographic assessment of sacroiliitis. Clinical and laboratorial data were taken into account to classify patients as fulfilling or not ASAS criteria for axial SpA. Clinical and demographic data were analyzed about their association with presence of ASAS criteria of axial SpA in an univariable logistic regression analysis. Variables with a p-value <0.05 were re-tested in a multivariable logistic regression. Those variables that maintained statistical significance were tested alone in another multivariable model. Analyses were performed with IBM SPSS Statistics (version 20.0). Regarding the 233 patients included, only 42 patients (19.4%) fulfilled ASAS criteria for axial SpA. However, 22 patients had asymptomatic radiographic sacroiliitis according to modified New York criteria. The prevalence of asymptomatic sacroiliitis was 15.7% between patients without axial symptoms. In multivariable analysis, inflammatory back pain (IBP) [OR=25.111; 95% confidence interval (CI) = 8.770, 71.900, p-value <0.001], presence of HLA-B27 [OR=9.072; 95% CI=2.756, 29.860; p-value <0.001] and male gender [OR=3.767; 95% CI=1.264, 11.232; p-value = 0.017] were associated to axial involvement according to ASAS criteria. Axial SpA ASAS criteria are useful to identify axial involvement in PsA patients. This type of involvement is more common in males, in the presence of HLA-B27 and IBP. Axial disease should be systematically assessed in clinical practice, mainly in patients presenting with this clinical features.