title: Serum immunoglobulin G4 in giant cell arteritis and polymyalgia rheumatica.
abstract: OBJECTIVE
  To date, no specific serum marker for giant cell arteritis and polymyalgia rheumatica has been established in routine practice. Therefore, the aim of this study was to examine whether immunoglobulin G4 serum concentrations could be a potential biomarker for the differentiation of both diseases.
  
  
  METHODS
  Serum immunoglobulin G4 (IgG4) concentrations were measured in patients with giant cell arteritis (n=41) and polymyalgia rheumatica (n=27) by an in-house enzyme-linked immunosorbent assay. In the subgroup of untreated patients with disease activity (polymyalgia rheumatica n=27, giant cell arteritis n=19) additional parameters of T-helper 2 cell inflammatory responses were analysed.
  
  
  RESULTS
  IgG4-values above the prior determined cut-off value of 1400 μg/ml in giant cell arteritis were rare and also significantly less frequent in giant cell arteritis than in polymyalgia rheumatica patients (7.3% vs. 44.4%; p<0.001). The relative risk that patients with clinical features of PMR, presenting without elevated IgG4 levels, have simultaneously GCA was 5.8 compared to those patients with elevated IgG4 levels. In untreated patients absolute counts of eosinophilic leukocytes were lower in giant cell arteritis than in polymyalgia rheumatica (p=0.002) and the cytokines interleukin-4 (p=0.013) and interleukin-10 (p=0.033) were less frequently detectable in giant cell arteritis than in polymyalgia rheumatica.
  
  
  CONCLUSIONS
  In giant cell arteritis serum levels of IgG4 usually are within the normal range. In polymyalgia rheumatica however, increased IgG4 serum levels are frequently found. Normal IgG4 serum levels in polymyalgia rheumatica may have predictive value in identifying patients with additional, clinically non-apparent giant cell arteritis.
authors.affiliation: Department of Rheumatology and Immunology, Klinikum Bad Bramstedt, Bad Bramstedt, Germany. mara.burkel@gmx.de.
authors.forename: Mara
authors.initials: M
authors.lastname: Burkel
authors.affiliation: Department of Rheumatology and Immunology, Klinikum Bad Bramstedt, Bad Bramstedt, Germany.
authors.forename: Fabian
authors.initials: F
authors.lastname: Arndt
authors.affiliation: Department of Rheumatology and Immunology, Klinikum Bad Bramstedt, Bad Bramstedt; and Department of Internal Medicine I, University Hospital Schleswig-Holstein, Campus Kiel and Christian-Albrechts-University of Kiel, Germany.
authors.forename: Jan-Henrik
authors.initials: JH
authors.lastname: Schirmer
authors.affiliation: Department of Rheumatology and Immunology, Klinikum Bad Bramstedt, Bad Bramstedt; and Rheumazentrum Schleswig-Holstein Mitte, Neumünster, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Moosig
authors.affiliation: Department of Rheumatology and Immunology, Klinikum Bad Bramstedt, Bad Bramstedt; and Rheumazentrum Schleswig-Holstein Mitte, Neumünster, Germany.
authors.forename: Julia U
authors.initials: JU
authors.lastname: Holle
mesh_terms: D000368:Aged; D015415:Biomarkers / Q000097:blood; D003937:Diagnosis, Differential; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D013700:Giant Cell Arteritis / Q000097:blood* / Q000000981:diagnostic imaging / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood*; D008297:Male; D008875:Middle Aged; D011111:Polymyalgia Rheumatica / Q000097:blood* / Q000000981:diagnostic imaging / Q000276:immunology; D011237:Predictive Value of Tests; D015854:Up-Regulation
chemical_list: D015415:Biomarkers; D007074:Immunoglobulin G