Inflammation is responsible for systemic bone loss in patients with seropositive rheumatoid arthritis treated with rituximab

Background/Aims: We investigated the effect of rituximab on systemic bone metabolism in patients with seropositive rheumatoid arthritis (RA). Methods: Twenty seropositive patients with RA were enrolled and administered one cycle of rituximab. If RA became active for > 6 months after the first rituximab cycle, a second cycle was initiated; otherwise, no additional treatment was administered. Patients were divided into two groups according to the number of rituximab treatment cycles. Results: In patients treated with a second cycle, the total hip bone mineral density (BMD) was clinically low, whereas the serum levels of receptor activator of nuclear factor kappa-B ligand (RANKL) were increased at 12 months. BMD in patients treated with one cycle did not change at 12 months, whereas serum RANKL levels decreased at all time points. DAS28 activity improved in both groups from baseline to 4 months; however, from 4 to 12 months, DAS28 activity worsened in the group with the second cycle but remained stable in the group with one cycle. Conclusions: Systemic inflammation, reflected by increased disease activity, may be responsible for the increase in RANKL levels, which causes systemic bone loss in rituximab-treated patients with RA. Although rituximab affects inflammation, it does not seem to alter systemic bone metabolism in RA.