Background Autoantibodies in early rheumatoid arthritis (RA) have important diagnostic value. Anti citrullinated protein antibodies (ACPA) and rheumatoid factor (RF) are believed to be associated with more severe clinical outcomes, but the utility of both autoantibodies in the clinical follow-up of disease is controversial. It has recently been described that bone damage in early and even recent-onset RA is attributed to ACPAs, which form years before clinical symptoms start to emerge1.
Objectives To investigate the longitudinal course of immunological markers, ACPA and RF, during the first year after diagnosis of RA, to see their utility for the clinical follow-up. In addition, to assess if the baseline values of ACPA are associated with the severity of initial radiographic involvement.
Methods The study population was 52 patients diagnosed with early RA according to ACR-EULAR 2010 classification criteria, with ACPA positive. Serum samples at baseline, 3, 6 and 12 months were analyzed, and levels of ACPA, RF, C reactive protein (CRP) and erythrocyte sedimentation rate (ESR) were determined. Values of DAS 28, SDAI and HAQ were employed as clinical activity markers.To analyse the variations of the measured parameters, we expressed the values of each analytic and clinical parameter as “Variation Index” on the baseline value for each patient (VI (x month)=Value (x month)/Value (baseline)). The statistical study was made through canonical correlation analysis and linear regression. Radiographic damage was evaluated using Sharp scores modified by Van der Heijde. Comparisons between this score and ACPA levels and other serological markers were evaluated by Spearman correlation coefficient.
Results A high correlation between clinical markers and analytical variables is observed with a first canonical correlation of 0,96 (p<0,001) at 3 months and 0,89 (p<0,001) at 12 months. The correlation is mainly determined by the relation between DAS 28 and HAQ with CRP and ESR. A correlation between autoantibodies and clinical markers is not found. We show no significant radiological damage in our patients, despite all being ACPA positive. The Sharp score modified by Van der Heijde was measured in 47 patients, with values between 0 and 101 (mean: 24,76±24,54). We find no correlation between Sharp score and ACPA, RF, ESR and clinical activity markers, and a weak correlation between Sharp Score and CRP (Spearman Rho: 0,459; p=0,005)
Conclusions In our group of patients with early RA, repeated measurement of ACPA or RF during the first year after onset of RA does not offer major additional information. Their quantification would not be indicated for follow-up disease, which means a cost reduction in the Autoimmunity Laboratory. We find no correlation between radiographic damage and ACPA titers at diagnosis. So, although ACPA are associated with bone wound, this is independent of the levels of antibodies.
Hecht C, et al. Additive efect of anti-citrullinated protein antibodies and rheumatoid factor on bone erosions in patients with RA. Ann Rheum Dis 2015; 74: 2151–2156.
Disclosure of Interest None declared