AB0885 WHAT HAVE THE UNDIFFERENTIATED SPONDYLOARTHRITIS BECOME AFTER 17 YEARS OF FOLLOW-UP? AN ANALYSIS OF THE REGISPONSER AND REGISPON-3 REGISTRIES
Authors: M. Á. Puche-Larrubia, M. L. Ladehesa-Pineda, M. C. Ábalos-Aguilera, D. Ruíz-Vilchez, L. Berbel-Arcobé, X. Juanola-Roura, M. Arévalo, M. Moreno, R. Almodóvar, C. Pijoán-Moratalla, B. Joven-Ibáñez, M. Valero Expósito, V. García García, M. Moreno, E. T. Ornilla Laraundogoitia, A. Escudero-Contreras, E. Collantes-Estevez, C. López-Medina
Journal: Annals of the Rheumatic Diseases (2024)

<h3>Background:</h3> Undifferentiated spondyloarthritis (uSpA) refers to a clinical entity within the spectrum of spondyloarthritis (SpA) that does not meet the criteria for a specific subtype as per the ESSG criteria. U-SpA has been described as a potential early form of axial SpA (axSpA) and other specific subtypes. However, there exist discrepancies about the proportion of patients that actually change from this undifferentiated state to a more defined diagnosis over time. <h3>Objectives:</h3> a) To describe the current diagnoses (e.g. axial SpA (axSpA), peripheral SpA (pSpA), Psoriatic Arthritis (PsA), or others) among patients diagnosed with u-SpA 17 years ago; b) To analyse the factors linked to the change in diagnosis among patients initially diagnosed with u-SpA. <h3>Methods:</h3> Longitudinal and multicentre study where patients with SpA (according to the ESSG Criteria) from REGISPONSER (assessed in 2004) were re-evaluated 17 years later (2021-2022), resulting in the REGISPON-3 study. REGISPONSER dataset has been combined with the REGISPON-3 data obtaining two visits separated by 17 years. Firstly, a descriptive analysis has been carried out to describe the change in the diagnosis of the u-SpA patients 17 years later according to the rheumatologist's criteria. Secondly, we studied what the diagnostic changes consist of according to some clinical characteristics and the presence of HLA-B27 using Chi-squared test. <h3>Results:</h3> A total of 64 patients diagnosed with u-SpA in 2007 were included in this analysis. Table 1 shows how the diagnosis of u-SpA has changed 17 years later. Among the 64 patients with u-SpA, 49 (76.5%) developed axSpA, 7 (10.9%) pSpA, 4 (6.2%) PsA and 4 (6.2%) finally did not have SpA according to the rheumatologist. Table 2 shows the change of the diagnosis of u-SpA according to some clinical characteristics and the presence of HLA-B27. Patients that change to axSpA were more frequently men [26 (53.1%)], HLA-B27 positive [41 (83.7%)], without peripheral joint disease [16 (32.7%)], and without psoriasis [47 (95.9%)], although statistical differences were only found for psoriasis. On the contrary, patients that changed to PsA were more frequently women [3 (75%)], but the prevalence in peripheral joint disease [2 (50%)] and psoriasis [2 (50%)] were similar with no significant differences. Patients who were eventually considered not to meet SpA criteria were more frequently women [4 (100%)], without arthritis [3 (75%)] and without psoriasis [0 (0%)]. <h3>Conclusion:</h3> The diagnosis of u-SpA varies over time, with axSpA being the type most frequently diagnosed in our study 17 years later. Patients without psoriasis and HLA-B27 positives were more frequently diagnosed with axSpA. <h3>REFERENCES:</h3> <b>NIL.</b> <b>Table 1.</b> Description of the evolution of u-SpA diagnosis over 17 years from REGISPONSER I-II to REGISPON-3 AS: ankylosing spondylitis; PsA: psoriatic arthritis; u-SpA: undifferentiated spondyloarthritis; r-AxSpA: non-radiographic axial spondyloarthritis; r-AxSpA: radiographic axial spondyloarthritis. <b>Table 2.</b> Change of the diagnosis of u-SpA according to clinical characteristics and the presence of HLA-B27 u-SpA: undifferentiated spondyloarthritis; r-AxSpA: non-radiographic axial spondyloarthritis; r-AxSpA: radiographic axial spondyloarthritis. Sex: p=0.153; HLA-B27: p=0.459; peripheral joint disease: p=0.216; psoriasis: p=0.003**. <h3>Acknowledgements:</h3> <b>NIL.</b> <h3>Disclosure of Interests:</h3> <b>None declared.</b>