Anti-cyclic citrullinated peptide antibody in systemic sclerosis.

OBJECTIVES To determine if anti-cyclic citrullinated peptide (anti-CCP) antibody titers can distinguish the overlap syndrome of systemic sclerosis and rheumatoid arthritis (SSc-RA) in patients with systemic sclerosis (SSc) and to investigate the clinical significance of anti-CCP antibodies in SSc. METHODS Serum levels of anti-CCP antibodies were measured by enzyme-linked immunosorbent assay in 159 outpatients: 114 with SSc, 14 with rheumatoid arthritis, 7 with SSc-RA overlap syndrome, and 24 with Sjögren's syndrome. In patients with SSc and SSc-RA, we also measured serum levels of matrix metalloproteinase-3 and anti-agalactosyl IgG antibody. RESULTS Elevated serum levels of anti-CCP antibodies were observed in 3 of 114 patients (2.6%) with SSc, 9 of 14 patients (64%) with RA, 6 of 7 patients (86%) with SSc-RA, and only 1 of 24 patients (4.2%) with SjS. In patients with SSc-RA, serum anti-CCP antibody levels were significantly higher than those seen in SSc (p<0.001). The sensitivity, specificity, and predictive values of elevated anti-CCP titers for SSc-RA were higher than either matrix metalloproteinase-3 and anti-agalactosyl IgG antibodies as markers. In addition, almost all SSc-RA and SSc patients with elevated serum levels of anti-CCP antibodies exhibited arthralgias and interstitial pneumonia. CONCLUSIONS Anti-CCP antibody titers are a reliable marker of SSc-RA facilitating its distinction from SSc alone.