Objectives: It is still controversial whether autoantibody (AAb) serum levels have a value for response monitoring in rheumatoid arthritis (RA). Therefore, we retrospectively investigated a real-life outpatient RA cohort to determine which factors are associated with change in serum AAb levels and RA disease activity. The primary goal of the study was to determine predictors for changes in DAS28 and autoantibodies over time and identify traits of non-rituximab treated patients, which would define strong association of disease activity with changes in AAb-levels.
Methods: Seventy-eight patients with seropositive RA were monitored for DAS28, CRP, ESR, anti-cyclic citrullinated peptides (CCP), anti-mutated citrullinated vimentin (MCV), and rheumatoid factor (RF). Using linear mixed regression modelling, factors influencing DAS28 and serum AAb were determined. Patients showing above (good correlators) and below (bad correlators) average correlation of serum AAb with DAS28 were further characterised.
Results: In non-rituximab treated patients (88.5%), associations of changes in AAb and DAS28 were strengthened with more morning stiffness (p=0.002), DMARD use (p=0.02), tender joints (p=0.01), swollen joints (p<0.01), higher ESR (p<0.01) and VAS (p<0.001) at baseline. Decrease of anti-CCP was also predicted by longer disease duration (-4.4 U/ml per year disease duration, p=0.048) and/or no erosions (-2.0 U/ml/month, p<0.01) at baseline, whereas erosive disease predicted an increase (+1.4 U/ml/month, p=0.015) in anti-CCP. Conversely, patients with erosive disease showed a trend to decrease RF (-1.9 U/ml/month, p=0.06).
Conclusions: In non-rituximab treated RA patients, the association between disease activity and change in autoantibody levels is not static, but strengthens with increase in signs of inflammation (ESR, VAS, swollen joints, tender joints, morning stiffness) at baseline. Therefore, studies of changes in AAb need to consider baseline inflammation as confounder.