A longitudinal study of anti-RNA polymerase III antibody levels in systemic sclerosis

Objectives. Anti-RNA-polymerase antibodies (ARAs) are associated with the diffuse cutaneous subset of SSc (dcSSc) and particularly with scleroderma renal crisis (SRC). We analysed serial ARA levels and explored the relationship with clinical features and disease outcome. Methods. A commercially available ELISA method with a recombinant peptide of RNA polymerase III was used and ARA levels were measured in a well-characterized cohort of SSc cases. Results. ARA levels were measured in 64 SSc patients. Of them, 78% (n=50) were females and 92% (n=59) had dcSSc, 39% (n=25) had SRC, 20% (n=13) had pulmonary fibrosis (PF), 9% (n=6) had pulmonary arterial hypertension and 3% (n=2) had cardiac involvement. There was considerable inter- and intra-patient variability in ARA levels (11-210 U/ml). There was no correlation between absolute ARA levels (at baseline or throughout the disease course) and outcome. There was a moderate correlation between time to peak ARA level and development of significant PF (Pearson correlation=0.669, P=0.034), but no correlation between peak ARA levels and onset of SRC. ARA levels change correlated with change in skin score (correlation coefficient within Subjects=0.236, P=0.011). Conclusions. The pathogenic significance of ARA is unclear. Despite the very strong association of ARA with SRC, we could not show the clinically significant association between absolute levels of antibody and development of internal organ complications, which makes repeated measurements of ARA levels unnecessary. However, changes in ARA level over time occur and may reflect changes in skin score.