The Impact of Seropositivity on Bone Mineral Density in Rheumatoid Arthritis - A 3-year Prospective Observational Study

Background:To explore the impact of seropositivity on systemic bone loss in rheumatoid arthritis (RA).Methods:This was an interim analysis of the RA registry. Clinical characteristics in the registry were documented, and bone mineral density (BMD) was measured; this was repeated 3 years later. Participants were grouped into seropositive (SPRA) and seronegative (SNRA) based on the presence or absence of rheumatoid factor (RF) and/or anti-cyclic citrullinated peptide antibodies (ACPA). After matching (1:2) for age and sex, SNRA and SPRA were regrouped into A and B. To elucidate the impact of number of antibodies on BMD changes, the matched group was sub-divided according to the number of antibodies present (0, group I; 1, group II; 2, group III). The changes in BMD were compared for each group at baseline and 3 years later. Results:A total of 477 participants who completed a 3-year observation period were included. After matching, 312 participants were enrolled (group A, 104; group B, 208). Three years later, group B had significant bone loss in the femoral neck (FN) (p <0.001), total hip (TH) (p = 0.001), and 1st–4th lumbar vertebrae (L1–4) (p = 0.006), while group A has bone loss only at FN (p = 0.002). Groups I, II, and III included 104, 52, and 156 participants, respectively. Significant bone loss was recorded at FN (p = 0.002) in group I, FN (p <0.001) in group II, and FN (p <0.001), TH (p = 0.002), and L1–4 (p = 0.016) in group III. In terms of percent change in BMD (△BMD%), more significantly negative changes were found at TH in group B (p = 0.027) and within groups I-III (p for trend = 0.021). Logistic regression showed that seropositivity is a significant predictor of △BMD≧–5% at TH (odds ratio 1.85, 95% confidence interval 1.03-3.33, p = 0.039).Conclusions:SPRA lost more bone than SNRA after 3 years. More attention should be paid to SPRA patients, especially those with double-positive antibodies, with vigorous evaluation of BMD and fracture risk.