Bone Abstracts

Introduction: Osteoporosis and fragility fractures are recognized complications of rheumatoid arthritis (RA). Previously Riches et al. described a patient with celiac disease and severe osteoporosis in whom neutralizing antibodies to osteoprotegerin (OPG) were present. The aim of this study was to determine if OPG autoantibodies were present in patients with RA and other rheumatic diseases and to relate these to clinical features.

Methods: We developed a novel ELISA to detect OPG autoantibodies, using recombinant human OPG as the capture antigen with detection of antigen-antibody complex through HRP conjugated anti-human antibodies. We screened for the presence of OPG autoantibodies in 75 patients with RA, 47 with SLE, 31 with spondyloarthritis (SpA) (21 AS, 10 Psoriatic Arthritis) and 200 age and sex matched healthy controls. OPG antibodies were considered to be present when values were > 3 S.D. above the mean in controls.

Results: Two patients in the control group (1%) had detectable OPG antibodies when compared with 7/75 patients with RA (9.3%, P=0.01 compared with controls), SpA n=8/3 (25.8%, P=0.01 from controls) and SLE n=3/49 (8%, P=0.05 from controls). In the RA group the presence of OPG antibodies was associated with disease duration and DAS28 score, but not with BMD (Table 1). No association was found between antibody levels and BMD and disease activity (BASDAI) in AS, or BMD in the other disease groups (not shown).

Conclusions: We conclude that OPG antibodies can be detected in a variety of autoimmune diseases. They are particularly common in SpA but also found in RA where they are associated with duration of disease and disease activity. Further research is in progress to evaluate the functional activity of OPG antibodies identified in patients with rheumatic diseases, and correlate this with clinical outcomes.