A case of μ heavy-chain disease associated with hyperglobulinemia, anemia, and a positive Coombs test

Abstract

 We report here for the first time a patient with μ heavy-chain disease (HCD), hyperimmunoglobulinemia, and a positive direct antiglobulin test (DAT, Coombs test). The heavy-chain diseases involve the proliferation of lymphoplasma cells of B cell origin and are characterized by the production of incomplete heavy chains devoid of light chains. The association of μ heavy-chain disease with either hyperglobulinemia or a positive DAT has not been reported in the literature to date. In this patient, immunofixation of serum proteins with monospecific antisera to α-, γ-, μ,- or δ-chains and to κ- and λ-chains revealed a precipitation band with antibody to IgM, but not with κ and λ light-chain antibodies, indicating μ heavy-chain disease. Hyperglobulinemia was present, which is very uncommon for HCD. A DAT of the patient's red blood cells (RBC) was found to be strongly positive for anti-IgG but negative for anti-IgM, -IgA, -C3c, and -C3d. However, when the eluate from the patient's red blood cells was investigated with nephelometry, it was found to contain antigens reactive with anti-γ as well with anti-μ-antiserum. When a DAT was performed with a randomly chosen test cell incubated with the eluate, the antibody-containing eluate was shown to react with anti-IgG as well as with anti-IgM-antiserum. In summary, the eluate from the patient's RBCs contained IgG and an immunoglobulin structure reactive with anti-IgM in an RBC agglutination assay as well as with anti-μ antiserum in a nephelometric investigation. Whether this IgM on the patient's erythrocytes is penta- or oligomeric, complete IgM, or the heavy chain cannot be concluded from these observations.