Features of the synovium of individuals at risk of developing rheumatoid arthritis
This study expands on previous findings that synovial inflammation does not coincide with the appearance of rheumatoid arthritis. This was a markedly larger study compared to previous, with 55 individuals assessed. All 55 subjects were positive for IgM rheumatoid factor and/or anti-citrillinated protein antibody as well as possessing no physical evidence of arthritis. 15 of the individuals tested developed arthritis after a median time of 13 months. In these patients the presence of inflammatory cells in the synovial tissue was not associated with arthritis development; consistent with this, MRI scans showed no indication of synovitis. Subclinical synovitis is not generally present more than one month before clinical manifest disease, indicating that it occurs relatively late in the pathogenesis of the disease. However, there was an increased trend toward increased T cell numbers in the synovium of patients who developed RA. These changes may be observed several months or even years before arthritis onset, as shown by the detection of ACPAs and IgM rheumatoid factor in the studied patients. The author propose a model in which systemic autoimmunity may exist years before the onset of RA and that a second event i.e an infection or trauma leading to citrullinated antigen expression might be needed for the development of arthritis.