Plasma cell (Zoon) balanitis: another inflammatory disorder that can be rich in IgG4+ plasma cells

Numerous IgG4 plasma cells and a high IgG4/IgG plasma cell ratio are important criteria in the diagnosis of IgG4-related sclerosing disease (IgG4-RSD), a steroid-responsive fibroinflammatory disorder. There is also a growing list of other inflammatory disorders that may mimic IgG4-RSD with many IgG4 plasma cells; however, limited data exist concerning whether plasma cell (Zoon) balanitis (PCB) is among these disorders. We, therefore, reviewed the clinical, histologic, and immunohistochemical features of PCB in 17 patients, including evaluation of CD3, CD20, CD138, κ, λ, IgG, IgG4, IgM, IgA, and IgD. All biopsies showed an infiltrate rich in plasma cells with variable numbers of B and T cells. IgG4 counts in the areas with the greatest density varied from 1/HPF to >200/HPF. Six of 17 (35.3%) cases demonstrated 50 or more IgG4 plasma cells/HPF, with an IgG4/IgG ratio of >40%, at least focally, in 2 of these cases. The plasma cells were clearly polytypic in 12/15 evaluable cases, with an increased proportion of κ-positive plasma cells in 3 (≥4 to 5:1). None of the patients had other clinical evidence of IgG4-RSD or a lymphoproliferative disorder. In conclusion, this study demonstrates that PCB should be added to the growing list of inflammatory disorders that can have significantly increased IgG4 plasma cells but which do not represent IgG4-RSD and which can have increased κ-positive plasma cells in the absence of malignant lymphoma.