OP0322 UNDERSTANDING AXIAL PSORIATIC ARTHRITIS IN CLINICAL PRACTICE - DATA FROM REUMA.PT
Authors: C. Abreu, V. Fraga, M. Diz Lopes, S. F. Azevedo, C. Vilafanha, J. Rovisco, I. Almeida, M. Pontes-Ferreira, H. Parente, A. Cunha, C. Dantas Soares, D. Medeiros, C. Cortesao, D. Augusto, M. Sebastiao, L. Silva, T. Meirinhos, J. Silva-Dinis, F. Araújo, J. Tavares-Costa, A. Vilar, A. Castro, M. J. Santos
Journal: Annals of the Rheumatic Diseases (2024)

<h3>Background:</h3> Psoriatic Arthritis (PsA) is part of the spectrum of spondyloarthritis (SpA), a diverse group of inflammatory arthropathies involving the sacroiliac, spine and peripheral joints. PsA can be categorized as either axial or predominantly peripheral disease. Axial Psoriatic Arthritis (axPsA) may occur exclusively or concomitantly with peripheral involvement. The prevalence of exclusive axPsA is estimated at 5% of patients increasing to 25-70% when associated with peripheral arthritis. However, the absence of a consensus definition for axPsA makes the real prevalence difficult to estimate. <h3>Objectives:</h3> 1) determine the proportion of axPsA among PsA patients and understand how it is diagnosed in clinical practice; 2) identify clinical and demographic characteristics associated with axPsA. <h3>Methods:</h3> Adult patients with the diagnosis of PsA or the diagnosis of axSpA with psoriasis registered in the Rheumatic Diseases Portuguese Registry (Reuma.pt) and fulfilling CASPAR criteria were included. Axial involvement was defined as either physician-reported spondylitis or the presence of imaging findings suggestive of axial involvement (radiographic sacroiliitis (SI) according to modified New York Criteria (mNYC), SI in magnetic resonance imaging (MRI), or the presence of syndesmophytes in axial radiography). Bivariate and multivariate analysis were performed to identify demographic and clinical characteristics associated with the diagnosis of axPsA. <h3>Results:</h3> A total of 2304 patients were included. The prevalence of axPsA was 37.1% (N=854), with 21.8% (N=186) having exclusive axPsA and 78.2% (N=668) having concomitant peripheral involvement. The diagnosis of axPsA was made based on suggestive imaging findings in 30.1% of patients, with radiographic SI being the most common (N=195; 75.9%) followed by the presence of syndesmophytes (N=93; 36.2%) and SI on MRI (N=54; 21%). In the remaining 69.9% of cases, spondylitis was physician-reported (imaging exams inaccessible). axPsA was associated with male sex (OR=1.54; 95% CI 1.30-1.81; p&lt;0.001), positivity for HLA-B27 (OR=3.5; 95% CI 2.64-4.65; p&lt;0.001), a younger age at diagnosis (42.9 ± 12.9 vs 46.2 ± 12.5; p&lt;0.001) and at symptom onset (38.5 ± 13 vs 43.0 ± 12.7; p&lt;0.001) (Table 1). Regarding extra-articular manifestations, axPsA was associated with a higher proportion of enthesitis (OR=1.61; 95% CI 1.33-1.96; p&lt;0.001), uveitis (OR=4.17; 95% CI 2.71-6.41; p&lt;0.001), psoriasis (OR=1.78; 95% CI 1.02-3.1; p=0.041) and inflammatory bowel disease (OR= 6.07; 95% CI 2.45-15.04; p&lt;0.001) and lower proportion of dactylitis (OR=0.72; 95% CI 0.59-0.87; p&lt;0.001) and nail dystrophy (OR=0.78; 95% CI 0.65-0.94; p=0.008). Current or previous tobacco exposure and alcohol consumption were also associated with axPsA (OR=1.41; 95% CI 1.15-1.73; p=0.001 and OR=1.46; 95% CI 1.17-1.83; p&lt;0.001, respectively). Patients with axPsA started therapy with first bDMARD at younger age (46.6 ± 11.8 vs 48.8 ± 11.1; p&lt;0.001), however the time from symptom onset until start date of first bDMARD was longer (7 (12) vs 6 (9) years; p=0.003). Multivariate analysis identified HLA-B27 positivity, enthesitis, lower prevalence of dactylitis and tobacco exposure as independently associated with axPsA. <h3>Conclusion:</h3> The prevalence of exclusive axPsA was 8.1%, increasing to 37.1% when considered concomitant with peripheral involvement. The most common diagnosis was physician-reported spondylitis; however, when considering imaging findings, radiographic SI was the most prevalent. We cannot rule out the possibility of underdiagnosis of axPsA, particularly cases of subclinical disease, given the limited availability of imaging exams. Patients with axPsA exhibited distinct clinical and laboratory features compared to peripheral PsA, with a higher prevalence of HLA-B27 positivity, enthesitis and tobacco exposure, and lower prevalence of dactylitis. <h3>REFERENCES:</h3> <b>NIL.</b> <h3>Acknowledgements:</h3> <b>NIL.</b> <h3>Disclosure of Interests:</h3> <b>None declared.</b>