title: Increased immunoglobulin (Ig) G4-positive plasma cell density and IgG4/IgG ratio are not specific for IgG4-related disease in the skin.
abstract: OBJECTIVE
  Immunoglobulin (Ig) G4-related disease (IgG4-RD), a fibroinflammatory condition that can affect multiple organs, is suggested by lymphoplasmacytic inflammation, fibrosis, phlebitis, and increased IgG4+ plasma cell (PC) tissue density. In patients with suspected IgG4-RD and skin changes, skin biopsy may serve as a diagnostic screen or to supplement nondiagnostic visceral biopsy specimens. We aimed to determine whether increased cutaneous IgG4+ PCs or IgG4/IgG ratio is specific for IgG4-RD.
  
  
  METHODS
  We examined 50 mucocutaneous specimens representing seven PC-rich dermatoses and reactive PC-rich infiltrates with IgG and IgG4 immunohistochemical stains.
  
  
  RESULTS
  IgG4+ density exceeded 10 cells per high-power field in 22 (44%) of 50 specimens, representing six of seven diagnoses and reactive infiltrates. In five specimens (10%), the IgG4/IgG ratio exceeded 0.40.
  
  
  CONCLUSIONS
  Moderately elevated IgG4+ PC density or IgG4/IgG ratio is a nonspecific finding in the skin. In cutaneous biopsy specimens showing increased IgG4+ PCs, careful consideration should be given to clinical, serologic, and other histopathologic features before attributing clinical changes to IgG4-RD.
authors.affiliation: Dept of Laboratory Medicine and Pathology, Mayo Clinic, 200 First St SW, Rochester, MN 55905; Lehman.julia@mayo.edu.
authors.forename: Julia S
authors.initials: JS
authors.lastname: Lehman
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Smyrk
authors.forename: Mark R
authors.initials: MR
authors.lastname: Pittelkow
mesh_terms: D006801:Humans; D007154:Immune System Diseases / Q000175:diagnosis / Q000276:immunology*; D007074:Immunoglobulin G / Q000276:immunology*; D010950:Plasma Cells / Q000276:immunology*; D012871:Skin Diseases / Q000175:diagnosis / Q000276:immunology*
chemical_list: D007074:Immunoglobulin G
keywords: Anatomic pathology; Basic science; Dermatopathology