With interest we read the article by Hecht et al 1 who studied the associations of anticitrullinated peptide antibodies (ACPA) and rheumatoid factor (RF) with bone erosions in rheumatoid arthritis (RA). The background of this study was that ACPAs directed against citrullinated vimentin induce differentiation of osteoclasts, indicating that ACPA has a direct effect on bone resorption. 2 No biological data are available on whether RF also affects bone cells and, given the overlap between ACPA-positivity and RF-positivity, the authors wanted to distinguish the association between RF and bone erosions from the association between ACPA and bone erosions. In a crosssectional study, high-resolution peripheral quantitative CT (HR-pQCT) images of metacarpophalangeal (MCP) 2–4 joints of 238 patients with RA were made and groups of patients with different combinations of autoantibodies were compared. The authors observed mainly differences in erosive burden in patients with both antibodies compared with those without antibodies. In a subgroup analysis, they also reported a higher erosive burden in ACPA+/RF+ patients compared with ACPA+/RF− patients. Based on their findings the authors suggested that RF may act as an enhancer of bone loss in ACPA-positive patients.

HR-pQCT is an interesting tool that admits measuring the three-dimensional size of erosions in detail. Conventional hands and feet radiographs have the advantage of their availability to study higher number of patients and evaluate more joints than is possible with HR-pQCT. We hypothesised that if RF acts additively on the erosive disease burden in ACPA-positive patients with RA, this should also be detectable by conventional radiographs. Therefore, we performed the present analysis to further increase the comprehension of the effects of both ACPA and RF on bone destruction in RA.