POS1081 SERONEGATIVE RHEUMATOID ARTHRITIS (RA) – IS IT REALLY RA?

Background The 2010 rheumatoid arthritis (RA) classification criteria are intended for research purposes and of the disease not diagnostic purposes. It is however a tool which clinicians commonly use in everyday practice when evaluating patients with arthritis. clearly stated that synovitis should be better explained by another disease. However, some who classified as seronegative RA might still have an alternative diagnosis, such psoriatic arthritis, chronic gout or pseudogout, polymyalgia rheumatica etc. Misclassification has direct impact on treatment, prognosis follow up patients, but also projects. Increased attention constant re-evaluation embraced this group to avoid misclassification promote optimal treatment. Objectives To assess frequency potential diagnosis could explain Methods This observational cohort study including adult factor (RF) anti-cyclic citrullinated peptide (anti-CCP) negative (symptom duration < 1 year), based ICD-10-SE (M06.0, M06.0M), without typical radiographical changes, between 2015-2019 at Karolinska University hospital. Patients were identified from Swedish Quality Rheumatology register (SRQ) had minimum 2 years follow-up after diagnosis. Additional medical information was collected charts retrospectively. re-classified 6 different groups: G1: presence symptoms signs crystal (gout pseudogout), and/or hyperuricemia ultrasound x-ray changes; G2: PMR – fulfilment time before; G3: systemic inflammatory (SLE, myositis, sclerosis, etc); G4: cancer one year before diagnosis; G5: spondylarthritis (i.e. psoriasis development back pain, dactylitis +/- enthesitis); G6: no other than can polyarthritis. Results A total 229 received fulfilled (double-seronegativity absence changes) during included study. Approximately 85% least 3 50% 5 time. percentage subgroups described above were: G1 = 6.6%, G2 6.5%, G3 =3.1%, G4 =7.4%, G5 4.4% G6 =72%. Conclusion In almost third paramalignant phenomenon, being most common. vigilance subgroup seronegative, non-erosive important consideration differential diagnoses warrantied. References [1] Aletaha D, Neogi T, Silman AJ, et al. Rheumatoid criteria: American College Rheumatology/European League Against Rheumatism collaborative initiative. Arthritis Rheum. Sep;62(9):2569-81. [2] Paalanen K, Puolakka Nikiphorou E, Is true arthritis? nationwide (Oxford). 2021 May 14;60(5):2391-2395. doi: 10.1093/rheumatology/keaa623. Erratum in: 14;60(5):2493-2494. PMID: 33175968; PMCID: PMC8121445. Acknowledgements: NIL. Disclosure Interests Emma Birgersson Wettersand: None declared, Katerina Chatzidionysiou Grant/research support from: Research grant: Galapagos.