Objective: To determine the clinical significance of anti-RNA polymerase III antibody in systemic sclerosis (SSc).
Design: A point prevalence study of autoantibody to RNA polymerase III and longitudinal examination of its clinical significance in patients with SSc and in controls.
Setting: University medical center rheumatology practice.
Patients: Two hundred fifty-two consecutive new patients with SSc and 170 controls (150 patients with other connective tissue diseases and 20 normal volunteers).
Measurements: The presence of anti-RNA polymerase III antibody was determined by immunoprecipitation, immunoblotting, and immunodepletion studies.
Main Results: Serum specimens from 57 of the 252 patients with SSc (23%; 95% CI, 18% to 28%) reacted with RNA polymerase III, compared with none of the specimens from 170 controls (0%; 95% CI, 0% to 2%). In 40 of these 57 specimens, immunoprecipitation studies also showed the presence of RNA polymerase I or II, or both. Anti-RNA polymerase III antibody was detected in sera from 50 of the 111 patients (45%) who had SSc with diffuse cutaneous involvement (dcSSc), 7 of 114 patients (6%) who had SSc with limited cutaneous involvement, and none of 27 patients with an SSc overlap syndrome (P < 0.001). Among patients with dcSSc, anti-RNA polymerase III antibody was more common than antitopoisomerase I antibody (45% compared with 27%; P = 0.008). Patients with anti-RNA polymerase III antibody had a statistically significant higher mean maximum skin thickness score but statistically significant lower frequencies of telangiectasias, inflammatory myopathy, restrictive lung disease, and serious cardiac abnormalities than did patients with antitopoisomerase I antibody.
Conclusion: Anti-RNA polymerase III antibody is a new marker autoantibody for many patients who have SSc with diffuse or extensive cutaneous involvement.