[IgM myeloma: 6 cases and a review of the literature]

IgM myeloma is a rare plasma cell neoplasia, with an estimated incidence of 0.5% in patients with myeloma. Approximately, between 2 and 3.3% of IgM monoclonal gammopathy are IgM myeloma. Six unpublished cases of IgM myeloma, association of an IgM monoclonal gammopathy and an exclusive plasma cell neoplasia, are reported. Forty-six other cases have been found in the literature. The initial clinical characteristics of these patients are: sex-ratio of 1.1, mean age of 62 years, fatigue in 95% of the cases, bone pain in 80%, osteolytic lesions in 78%, fever in 13%, hepatomegaly and splenomegaly in 8%, lymphadenopathy in 10%, hemorrhagic diathesis in 35% and neurologic involvement in 18%. Initial biological features are: anemia in 62% of the cases, creatininemia greater than 20 mg/l in 10%, calcemia greater than 120 mg/l in 24%. Mean serum IgM level is 33 g/l, mean medullary plasmocytosis is 52%. 80% of the patients presented with IgM kappa and only 20% with IgM lambda. Proteinuria with light chains are found in 65%. One-year survival is estimated at 82%, 2-year at 62%, 3-year at 46% with a median of 30 months. No prognostic factor is found. IgM myeloma with characteristics of both myeloma and macroglobulinemia appears well individualized among B-cell neoplasia. However, the distinction between Waldenström's macroglobulinemia and IgM myeloma can be difficult in case of lympho-plasmocytic bone marrow proliferation with osteolytic lesions.