Is psoriatic arthritis really seronegative?

BackgroundPsoriatic Arthritis (PsA) is a heterogeneous disease classified as a seronegative group of inflammatory arthritis.ObjectivesOur aim was to understand the real-life seropositivity rates for commonly used autoantibodies in rheumatology practice in a cohort of PsA patients treated with biologic agents.MethodsPsA patients from the Hacettepe University biological database (HUR-BIO) were assessed for the anti-nuclear antibody (ANA), rheumatoid factor (RF), and anti-cyclic citrullinated peptide (CCP) before and after the initiation of biologic agents. Demographic characteristics, the interval between the test and biologic initiation, and the rates of seropositivity for individual tests, autoantibody titers, and subtypes for ANA were determined.ResultsFrom 520 PsA patients registered, results of 419 patients with at least one autoantibody tested either before or after biologic treatment is presented in Table 1. From the patients tested, 69% of them had at least one autoantibody positive and 30.8 % of them were triple negative before the biologic treatment. The rates reached to 78.7% of seropositivity for at least one autoantibody and 21.2 %triple negativity after treatment. ANA showed the highest rates of seropositivity among autoantibodies with a rate of 40% before and 55.3 % after biologic treatment. Concomitant seropositivity for RF and CCP autoantibodies showed rates of 2.8% and 6.3% before and after treatment, respectively. The most common subtype was AC4-5 before and AC1-4-5 after biologic agent treatment. ANA was tested in 31 patients both before and after biologic treatment showing 6 negative patients became positive after treatment and from 12 positive patients at the baseline 6 of them became negative (p=0.452). The most common biologic agents used in patients with ANA tested after treatment, were adalimumab (ADA) (42.4%), etanercept (ETN) (18.9%), and infliximab (IFX) (18.9%). The only difference was observed in IFX treated patients (n=25) with significantly higher rates of IFX usage in ANA-positive patients (p=0.001).Table 1.Demographics and ANA, RF, Anti-CCP test results of patients before and after biologic treatmentANARFAnti-CCPbDMARDs initiationBeforeAfterBeforeAfterBeforeAfterNumber of patients10413231027814497Age43.5 (12.7)46.7 (11.6)43.3 (12.5)47.9 (11.9)44.3 (12)48.6 (12.1)Female sex, n (%)84 (80.7)97 (73.5)225 (72.5)211 (75.8)110 (76.3)75 (77.3)Time interval between test and bDMARD initiation, months, median (IQR)7.4 (0.84-17.83)32.6 (14.93-72.33)4.1 (0.35-16.75)31.63 (13.10-64.08)3.23 (0.30-11.5)35.13 (12.40-75.43)Positivity, n (%)42 (40.4)73 (55.3)30 (9.6)32 (11.5)12 (8.3)11 (11.3)Titer IU/ml, median (IQR)NANA28.7 (22.35-98.5)28.9 (21.9-110)139.1 (20.38-250)67.5 (16.77-139)Titer, n (%) *28 (66.6)38 (52)N/AN/AN/AN/A1/1007 (16.7)14 (19.1)1/1607 (16.7)20 (27.3)≥1/320bDMARD: Biologic Disease Modifying Anti-Rheumatic Drugs, ANA: Anti-nuclear antibody, RF: Rheumatoid factor, Anti-CCP: Anti- Cyclic citrullinated peptide, F:Female, M:Male, IQR: Interquartile range, IU/ml: International units per milliliter, N/A: Not available*Subtype is not given for one patient in patients with positive ANA after biologic treatmentConclusionSynovial lymphoid neogenesis rates in PsA are similar to the frequency seen in rheumatoid arthritis (1). Nevertheless, PsA is classified under the group of “seronegative diseases”. On the other hand, current reports have started to define specific autoantibodies particularly in psoriasis patients (2). The real-life experience in serology results of PsA patients showed that only 20-30 % of the patients were seronegative for all three tests commonly used in practice.References[1]Celis R, et al. Synovial cytokine expression in psoriatic arthritis and associations with lymphoid neogenesis and clinical features. Arthritis Res Ther. 2012 Apr 27;14(2):R93.[2]Yuan Y, et al. Identification of Novel Autoantibodies Associated With Psoriatic Arthritis. Arthritis Rheumatol. 2019 Jun;71(6):941-951.Disclosure of InterestsNone declared