Relatively restricted migration of polyclonal IgG4 may mimic a monoclonal gammopathy in IgG4-related disease.

OBJECTIVES IgG4-related disease (IgG4-RD) is an increasingly recognized syndrome of unknown etiology that can affect a wide variety of organs. The commonly shared features include tumor-like swelling of the involved organs, a lymphoplasmacytic infiltrate enriched with polyclonal IgG4-positive plasma cells, variable degree of fibrosis, and elevated serum concentrations of polyclonal IgG4. METHODS In a qualitative retrospective study, the electrophoretic characteristics of serum from patients with increased polyclonal IgG4 were studied to see if a reproducible pattern could be identified. RESULTS We demonstrate that a characteristic focal band bridging the β and γ fraction by serum protein electrophoresis may be a first serologic indication for IgG4-RD. We further demonstrate that significant κ:λ skewing can occur in the polyclonal IgG4 fraction. CONCLUSIONS The focal band detected by electrophoresis in sera from patients with IgG4-RD can be confirmed as polyclonal by immunofixation or immunosubtraction. Because these bands may be predominately of one light chain isotype, they could be misinterpreted as monoclonal gammopathies.