title: Hypocomplementemia in systemic sclerosis--clinical and serological correlations.
abstract: OBJECTIVE
  Although complement fixation is not commonly thought to be part of the pathogenesis of systemic sclerosis (SSc), hypocomplementemia has been associated with SSc. We hypothesized that hypocomplementemia in SSc might indicate the presence of overlap disease. We investigated if SSc patients with hypocomplementemia had more features of overlap disease than those with normal complement levels.
  
  
  METHODS
  Study subjects consisted of those enrolled in the Canadian Scleroderma Research Group Registry. Patients were divided into 2 groups: those with normal complement levels (normal C3 and C4) and those with hypocomplementemia (low C3 or C4). Evidence of overlap disease was defined as physician reports of other specific rheumatic conditions. Autoantibodies were assayed. Differences in rates of concomitant diseases and in antibody profiles were compared between groups.
  
  
  RESULTS
  Our study included 321 patients (88% women, mean age 56 +/- 13 yrs, mean disease duration 11 +/- 9 yrs). Of these, 276 (86%) had normal complements and 45 (14%) had hypocomplementemia. Patients with hypocomplementemia were significantly more likely to have physician-reported inflammatory myositis (27% vs 12%; p < 0.008) and vasculitis (11% vs 2%; p < 0.011) than those with normal complement. There was also a trend toward more antichromatin antibodies (18% vs 9%; p = 0.051) in patients with hypocomplementemia compared to normals.
  
  
  CONCLUSIONS
  Hypocomplementemia may identify a particular subgroup of SSc patients who have overlap disease.
authors.affiliation: SMBD-Jewish General Hospital and McGill University, 3755 Cote Sainte-Catherine Road, Montreal, Quebec, Canada. marie.hudson@mcgill.ca
authors.forename: Marie
authors.initials: M
authors.lastname: Hudson
authors.forename: Jennifer G
authors.initials: JG
authors.lastname: Walker
authors.forename: Marvin
authors.initials: M
authors.lastname: Fritzler
authors.forename: Suzanne
authors.initials: S
authors.lastname: Taillefer
authors.forename: Murray
authors.initials: M
authors.lastname: Baron
mesh_terms: D000328:Adult; D000368:Aged; D001323:Autoantibodies / Q000097:blood; D002170:Canada; D015331:Cohort Studies; D003165:Complement System Proteins / Q000172:deficiency* / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012042:Registries; D012595:Scleroderma, Systemic / Q000097:blood* / Q000276:immunology* / Q000473:pathology / Q000503:physiopathology
chemical_list: D001323:Autoantibodies; D003165:Complement System Proteins