THU0383 PREVALENCE OF SPONDYLOARTHRITIS IN FIRST DEGREE RELATIVES OF PATIENTS WITH ANKYLOSING SPONDYLITIS

Abstract

Background Ankylosing spondylitis (AS) is a common rheumatic disease with higher prevalence in relatives of patients already diagnosed with the disease. Heritability of AS in twins is estimated to 90%. Objectives The aim of this study was to examine first degree relatives (FDR) of AS patients, to determine whether the patients already fulfil criteria for axial and/or peripheral spondyloarthritis (SpA) and compare the findings to healthy controls (HC). Methods We recruited 32 patients without prior rheumatologic diagnosis with first degree relative treated for AS and 20 age and sex matched HC. The clinical data were collected and rheumatology examinations were performed by trained rheumatologists. Magnetic resonance imaging (MRI) of sacroiliac joints (SIJ) was read by trained rheumatologist who was blinded to the patient’s data. Patients were further divided into the subsets of axial SpA (imaging and clinical arm) and peripheral SpA fulfilling The Assessment of SpondyloArthritis international Society (ASAS) classification criteria1 and subset of non-SpA. The ASAS modified Berlin algorithm for diagnosis of axial SpA2 (axSpA) was also applied. Results Altogether, 78% (n=25) FDR referred back pain, 34% (n=11) referred inflammatory back pain (IBP), and 22% (n=7) did not refer back pain, which was significantly different from that in HC (65% referred back pain, 0% referred IBP, 35% referred no back pain, p=0.0038 and p=0.03, respectively). Bone marrow edema (BME) was found in 50% (n=16) of FDR, and 22% (n=7) had highly suggestive BME3 (hsBME) corresponding to typical findings of active sacroiliitis compared to HC where 10% (n=2) had BME, and none had hsBME (p=0.063, p=0.035, respectively). Furthermore, FDR had higher BASDAI and higher prevalence of HLA-B27 positivity compared to HC (2.0 (±1.5) and 75% vs. 0.4 (±0.6) and 5%, p= 0.001 and p= 0.001, respectively), no other significant differences were observed. The diagnosis of SpA was confirmed in 37% (n=12) of all FDR, 25% (n=8) patients fulfilled the imaging arm and 6% (n=2) fulfilled the clinical arm of ASAS classification criteria for axSpA, 6% (n=2) patients fulfilled ASAS classification criteria for peripheral SpA. The diagnosis of axSpA according to the ASAS modified Berlin algorithm was confirmed in 41% (n=13) patients. Analysis of clinical characteristics showed significant difference between serum CRP levels in SpA vs. non-SpA (8.2 (±12.5) vs. 2.3 (±4.4), p=0.02, respectively) and HLA-B27 positivity (100% vs. 60%, p=0.01, respectively). Presence of back pain and inflammatory back pain were more often in SpA compared to non-SpA subsets (100% and 67% vs. 65% and 15%, p=0.03 and p=0.006, respectively). Conclusion More than one third of first degree relatives of patients with AS fulfilled the criteria for axial or peripheral SpA, and had significantly higher prevalence of inflammatory back pain and increased BASDAI compered to HC. Based on these data, screening of family members of patients with AS should be recommended.