Gamma Heavy Chain Disease Presenting in a Patient with Systemic Lupus Erythematosus Progressing to Diffuse Large B-Cell Lymphoma: Case Report and Review of the Literature

Abstract

Heavy chain disease (HCD) is a rare form of monoclonal gammopathies of undetermined significance (MGUS) characterized by deletions in heavy chain gene resulting in defective heavy chain protein that cannot bind to light chain to form complete Ig molecule. Gamma heavy chain disease (y-HCD) is a rare form of HCD, which is extremely rare, with fewer reported cases compared to other heavy chain diseases such as alpha heavy chain disease (associated with IgA) and mu heavy chain disease (associated with IgM). y-HCD is a rare B-cell lymphoproliferative disorder characterized by the secretion of a truncated hinge region of the B-cell immunoglobulin molecule by a malignant clone of plasma cells producing the heavy chain gamma isotype in the absence of accompanying light chains. The true incidence of this disease is not known, as there are likely many asymptomatic individuals. The clinical diagnosis requires demonstrating both a serum monoclonal protein (M-protein) that contains HC and an absence or low concentration of the corresponding intact immunoglobulin (Ig). The diagnosis of y-HCD is frequently delayed either because the patient has no symptoms or because the patient has symptoms for which there may be many differential diagnoses. We report the appearance of y-HCD in an SLE patient mainly characterized by later conversion to diffuse large B-cell lymphomas (DLBCLs). We also briefly review the pertinent literature on this uncommon.