INTRODUCTION Waldenström macroglobulinemia (WM) is a distinct clinicopathological entity resulting from the accumulation, predominantly in the bone marrow, of clonally related lymphocytes, lymphoplasmacytic cells, and plasma cells that secrete a monoclonal immunoglobulin M (IgM) protein (Figure 11.1). This condition is considered to correspond to the lymphoplasmacytic lymphoma (LPL) as defined by the Revised European American Lymphoma (REAL) and World Health Organization classification systems. Most cases of LPL are WM, with less than 5% of cases made up of IgA, IgG, and nonsecreting LPL. EPIDEMIOLOGY AND ETIOLOGY WM is an uncommon disease, with a reported age-adjusted incidence rate of 3.4 per million among males and 1.7 per million among females in the United States, and a geometrical increase with age. The incidence rate for WM is higher among Caucasians, with African descendants representing only 5% of all patients. Genetic factors appear to be an important factor to the pathogenesis of WM. Approximately 20% of WM patients have an Ashkenazi (Eastern European) Jewish ethnic background, and there have been numerous reports of familiar disease, including multigenerational clustering of WM and other B-cell lymphoproliferative diseases. In a recent study, approximately 20% of 257 serial WM patients presenting to a tertiary referral had a first degree relative with either WM or another B-cell disorder. Frequent familiar association with other immunological disorders in healthy relatives, including hypogammaglobulinemia and hypergammaglobulinemia (Particularly polyclonal IgM), autoantibody (Particularly to thyroid) production, and manifestation of hyperactive B cells have also been reported.
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