Background/Purpose: The finding of circulating biomarkers in the field of chronic arthritis is still an unmet need, especially for the subgroup of seronegative arthritis [e.g., negative for anti-citrullinated peptides autoantibodies (ACPA) and/or rheumatoid factors (RF)]. In fact, in this clinical subset, there is a lack of soluble molecules which could help for a diagnostic or prognostic purpose, and the differential diagnosis between psoriatic arthritis (PsA) and seronegative rheumatoid arthritis (RA) may still be a challenge. C-X-C motif chemokine 13 (CXCL13) is one of the most promising biomarkers identified, because of its association with active synovitis (Bechman et al. BMC Rheumatology 2020) and with a poor prognosis in RA (Bugatti et al. Rheumatology 2014), although there are still inadequate results to justify its routine use. No data are available of the determination of CXCL13 serum levels in PsA. The aim of this study was to analyse CXCL13 serum levels in a cohort of PsA patients with a history of peripheral involvement in comparison with RA.

Methods: Cross sectional analysis of consecutive patients with peripheral PsA [n:81; male/female=44/37; median age (25°-75° percentile)=54 (46-62) years; 28-joint Disease Activity Score-C Reactive Protein (CRP-DAS28)=1.9 (1.6-2.5); active psoriasis=43%; DAPSA (Disease Activity in PSoriatic Arthritis) score=8 (3-14)] and RA [n:143; male/female=30/113; age =62 (50-70) years; seropositive=67%; CRP-DAS28=2.1 (1.5-2.8)] was performed. 100 sex and age-matched healthy controls (HC) were enrolled. CXCL13 serum levels were assessed through commercial ELISA test (R&D).

Results: CXCL13 serum levels were higher in all the subgroups of patients [PsA: 50.9 (34.5-80.2) pg/mL, p< 0.01; RA: 77.2 (52.9-107.7) pg/mL, p< 0.01; RA ACPA+: 77.7 (55.9-110.7) pg/mL, p< 0.01; RA ACPA-: 69.5 (49.3-104) pg/mL, p< 0.01] than in HC (22.3 (17.7-33.8) pg/mL). No significant differences were found among RA patients according with their seropositivity (p=0.378). CXCL13 serum levels were lower in PsA patients than in RA patients, independently from their seropositivity [vs RA ACPA+, p< 0.01; vs RA ACPA-, p=0.012]. CXCL13 serum levels were positively correlated with CRP in PsA patients (r=0.30; p=0.008), but not with DAPSA score.

Conclusion: These results confirm the value of CXCL13 as a biomarker in the field of chronic arthritis. Its higher levels in seronegative RA than in PsA suggests its possible value in the differential diagnosis of these two subsets of arthritis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-potential-diagnostic-value-of-c-x-c-motif-chemokine-13-cxcl13-in-seronegative-arthritis/