Among the 435 seronegative cases (69 % women, baseline mean age was 59 years), 13 (13/435 [3%]) could be reclassified as seropositive or erosive RA: 4 turned seropositive (2 for ACPA and 2 for RF [> 2x reference level]) and 9 developed erosions typical for RA.
Presence of the anti-CarP antibodies in sera of RA patients may have a prognostic value as it correlates with the disease activity and joint erosions; moreover, it may have a diagnostic value in rheumatoid arthritis especially in RF- and ACPA-negative patients.
In the placebo, every 6 months, every 3 months and every 2 months groups, the mean changes in the erosion score, according to the RF status (RF-positive vs -negative subgroups), were 1.18 vs 0.59, 0.25 (P = 0.0601 vs placebo) vs 0.31 (P = 0.0827), 0.21 (P = 0.0422) vs -0.02 (P = 0.0631) and 0.15 (P = 0.0010) vs -0.05 (P = 0.0332), respectively, while the mean changes in the erosion score, according to the ACPA status (ACPA-positive vs -negative subgroups), were 1.30 vs 0.07, 0.26 (P = 0.0142) vs 0.33 (P = 0.2748), 0.16 (P = 0.0058) vs 0.08 (P = 0.7166) and 0.09 (P < 0.0001) vs 0.08 (P = 0.8939), respectively.
A meta-analysis of ESPOIR and RMP cohorts confirmed that the carriage of AC haplotype was significantly associated with the rate of erosions at 1 year in the whole sample (OR[95%CI] = 1.92[1.14-3.22], p = 0.01) and in ACPA positive patients (OR[95%CI] = 3.34[1.68-6.67], p = 0.0006).
Hormonal treatment exposition and smoking were found to act with a protective effect against ACPA production (OR = 0.44, 95% CI 0.3, 0.7, P = 0.001) and early bone erosion (OR = 0.56, 95% CI 0.4-0.8, P = 0.003), respectively, and independently of HLADR and PTPN22 status.
ACPA-negative RA with apparent bone erosion was not associated with SE, supporting the idea that ACPA-negative RA is genetically distinct from ACPA-positive RA.