Gamma-heavy chain monoclonal gammopathy with undetermined significance (MGUS)

Gamma-heavy chain disease (γ-HCD) is a rare B-cell tumor producing truncated IgG lacking the light chain. The clinical features of γ-HCD are heterogeneous, similar to lymphoplasmacytic lymphoma, and most patients have generalized and progressive disease. In some γ-HCD patients, autoimmune diseases are associated. Thus, γ-HCD as a restricted or indolent disease is exceptional. A 66-year-old male was referred to our hospital because of subungual hemorrhage at the bilateral halluces. Physical and laboratory examination results were nonspecific, and the hemorrhage was revealed to be traumatic. However, serum electrophoresis demonstrated a small M-peak, which was monoclonal IgG-Fc without the corresponding light chain on immunofixation and immunoelectrophoresis. Bone marrow aspirate demonstrated a small number of lymphoplasmacytic cells that were positive for CD19, CD38, CD138, and cyIgG, but negative for cyκ- and -λ light chains on flow cytometry. A diagnosis of γ-HCD was made. Chest and abdominal CT demonstrated neither hepatosplenomegaly, lymphadenopathy, nor bone lytic lesions. The serum concentrations of IgG and M-peak configuration have remained relatively unchanged for nearly 3 years. Therefore, this γ-HCD may correspond to a rare form of monoclonal gammopathy with undetermined significance.