SAT0579 Presence of autoantibodies in erosive hand osteoarthritis and association with clinical presentation
Authors: M.A. van Delft, S. Van Beest, M. Kloppenburg, L.A. Trouw, A. Ioan-Facsinay
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> One of the most prevalent clinical phenotype of osteoarthritis (OA) is hand OA (HOA), which in some patients can evolve to erosive HOA. In erosive HOA central erosions and subchondral destruction are seen, and imaging studies have indicated that in erosive HOA hand joints display more inflammatory signs than in non-erosive HOA. Autoantibodies directed against post-translationally modified proteins, such as citrullinated (ACPA) and carbamylated (anti-CarP antibodies) proteins, are a hallmark of rheumatoid arthritis (RA), and are associated with more severe joint damage and inflammation. Interestingly, these antibodies are present in a small subset of SLE patients as well, in which they associate with bone erosions. This suggests the possible involvement of autoantibodies in inflammation and joint damage in other conditions than RA. Therefore, we hypothesised that autoantibodies are present in HOA and associate with erosive disease. <h3>Objectives</h3> To investigate whether three RA-associated antibodies, Rheumatoid Factor (RF), ACPA and anti-CarP antibodies, are present in hand OA and associate with erosive OA. <h3>Methods</h3> Anti-CarP IgG, ACPA IgG and RF IgM were measured by ELISA in baseline sera of HOA patients from 3 cohorts: HOSTAS (n=510, mean age 61.0 years, 85.7% women, 27.2% EOA), ECHO (n=47, mean age 63.4 years, 89.4% women) and EHOA (n=23, mean age 57.1 years, 73.9% women), and in sera of healthy controls (HC; n=196, mean age 44.1 years, 51.0% women). The prevalence of autoantibodies was compared between HOA and HC and between erosive and non-erosive HOA. In HOSTAS, hand radiographs were scored (Kellgren-Lawrence, OARSI osteophyte and joint space narrowing scores) and C-reactive protein (CRP) levels, representing inflammation, were assessed. Groups were compared using non-parametric tests. <h3>Results</h3> In both ECHO and EHOA cohorts, only one patient was positive for RF IgM and none were positive for ACPA IgG. In all three cohorts, a low prevalence of anti-CarP IgG was detected and this was not different between HOA patients and HC (6.6% vs 3.6%, p=0.12). Moreover, in HOSTAS, the prevalence of all tested autoantibodies was low and not significantly different from HC (anti-CarP 7.1% vs 3.6%, p=0.08; ACPA 0.8% vs 1.5%, p=0.37; RF 6.1% vs 4.1%, p=0.30). Likewise, no difference was found between erosive and non-erosive HOA (anti-CarP 7.2% vs 7.1%, p=0.94; ACPA 0.7% vs 0.8%, p=0.92; RF 4.3% vs 6.5%, p=0.36). Radiographic damage and CRP levels were similar in anti-CarP positive vs negative, and RF positive vs negative HOSTAS patients. <h3>Conclusions</h3> The prevalence of autoantibodies is similar in HOA patients and healthy controls. Moreover, these autoantibodies are not associated with erosive disease, structural damage or inflammation in HOA patients, indicating that another mechanism is driving erosive disease. <h3>Acknowledgements</h3> We thank J.C. Kwekkeboom for her help in collecting the samples, C. Kromme for his help with designing the data file and W. Damman for her help in the scoring of the radiographs. <h3>Disclosure of Interest</h3> M. van Delft: None declared, S. Van Beest: None declared, M. Kloppenburg: None declared, L. Trouw Consultant for: Listed as inventor in a patent application regarding the detection of anti-CarP antibodies for rheumatoid arthritis, A. Ioan-Facsinay: None declared