title: Immunohistochemistry for immunoglobulin G4 on paraffin sections for the diagnosis of pemphigus.
abstract: BACKGROUND
  Pemphigus is a group of autoimmune vesiculobullous diseases characterized by immunoglobulin G (IgG) antibodies directed against desmosomal adhesion proteins, with IgG4 being the predominant subclass in active diseases. Direct immunofluorescence for IgG performed on fresh-frozen tissue plays a crucial role in diagnosing pemphigus. However, the diagnosis might be hindered when frozen tissue is not available.
  
  
  OBJECTIVE
  To evaluate the usefulness of immunohistochemistry for IgG4 performed on paraffin sections as a diagnostic test for pemphigus.
  
  
  METHODS
  Eighteen immunofluorescence-proven pemphigus cases (12 pemphigus vulgaris, 6 pemphigus foliaceus) were studied. Four normal skin specimens and 32 nonpemphigus vesiculobullous disease specimens served as controls. Paraffin sections of all cases were examined immunohistochemically for IgG4 expression. Positivity was defined as distinct, condensed, continuous immunoreactivity localized to the intercellular junctions of keratinocytes.
  
  
  RESULTS
  The immunostains were independently evaluated in a masked manner by 3 pathologists, with a 100% interobserver agreement. Nine of 12 pemphigus vulgaris cases (sensitivity 75.0%), and 4 of 6 pemphigus foliaceus cases (sensitivity 66.7%), were positive for IgG4 immunostain. The overall sensitivity was 72.2%. One control specimen (bullous pemphigoid) showed IgG4 positivity (specificity 97.2%). In specimens demonstrating acantholysis, 8 of 10 pemphigus vulgaris cases (sensitivity 80.0%) and 4 of 4 pemphigus foliaceus cases (sensitivity 100.0%) were positive for IgG4. The overall sensitivity for specimens with acantholytic lesions was 85.7%.
  
  
  CONCLUSIONS
  Immunohistochemistry for IgG4 provides a reasonably sensitive and highly specific test for diagnosing pemphigus, especially when frozen tissue is not available, and active acantholytic lesions are examined.
authors.affiliation: Department of Medicine (Dermatology), University of Chicago Medical Center, 5841 S Maryland Ave, MC5067, Chicago, IL 60637, USA.
authors.forename: Xuefeng
authors.initials: X
authors.lastname: Zhang
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Hyjek
authors.forename: Keyoumars
authors.initials: K
authors.lastname: Soltani
authors.forename: Vesna
authors.initials: V
authors.lastname: Petronic-Rosic
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Shea
mesh_terms: D001323:Autoantibodies / Q000378:metabolism; D016022:Case-Control Studies; D051183:Desmoglein 1 / Q000276:immunology; D051184:Desmoglein 3 / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism*; D007150:Immunohistochemistry; D016612:Paraffin Embedding; D010392:Pemphigus / Q000175:diagnosis* / Q000276:immunology* / Q000473:pathology
chemical_list: D001323:Autoantibodies; D051183:Desmoglein 1; D051184:Desmoglein 3; D007074:Immunoglobulin G