Prevalence and clinical profiles of 'autoantibody-negative' systemic sclerosis subjects.

OBJECTIVES: To determine the prevalence of autoantibody negative systemic sclerosis (SSc) and to identify the clinical correlates thereof. METHODS: Clinical data and sera from 874 SSc subjects were collected and autoantibodies were tested in a central laboratory using 1) indirect immunofluorescence (IIF), 2) commercially available ELISA, addressable laser bead immunoassay (ALBIA), and line immunoassay (LIA), and 3) a sensitive immunoprecipitation (IP) assay. RESULTS: Fifteen (15; 1.7%) subjects were autoantibody negative by IIF, ELISA, ALBIA, LIA and IP, and 16 (1.8%) were antinuclear antibody (ANA) positive by IIF but otherwise negative by ELISA, ALBIA, LIA and IP. Thirty-seven (37; 4.2%) were ANA positive by IIF, autoantibody negative by commercially available immunoassays, but had autoantibodies identified by IP (including Th/To in 20). Autoantibody-negative subjects had generally less severe disease than positive subjects. CONCLUSIONS: Autoantibody-negative SSc is rare (<2%) and appears to be associated with a favourable prognosis.