The lymphoproliferative disorders are malignant transformations of lymphocytes. The clinical syndromes corresponding to each diagnostic category result from the characteristic behavior of the transformed cell. The end stage of B-lymphocyte development is the plasma cell producing large amounts of immunoglobulin. The malignant transformation of cells with this degree of differentiation represents a group of diseases termed the plasma cell dyscrasias or plasma cell proliferative disorders.

A spectrum of clinical conditions exists from monoclonal gammopathy of uncertain significance to multiple myeloma, Waldenstrom’s macroglobulinemia, and amyloidosis. However, it is the production of immunoglobulin by a plasma cell that ties these diseases together.

Normal B-cell development involves production of one of the five classes of immunoglobulins. The earliest event in B-cell development involves rearrangement of the germline immunoglobulin genes to produce a unique immunoglobulin. Ultimately, a specific immunoglobulin of the IgM class is made. Subsequently, the cell is able to alter the class of immunoglobulin (IgG, -A, -D, -E) while retaining the unique antigenic recognition sites. Each clone of cells produces only one immunoglobulin with one heavy chain (G, A, M, E, D) and one light chain (kappa, lambda). Protein electrophoresis and immunoelectrophoresis can detect the production and secretion of these immunoglobulins or their components (a light chain or heavy chain). The abnormal accumulation of monoclonal immunoglobulin in the serum is frequently called an M spike and is usually one of the early clues to the diagnosis of plasma cell dyscrasias.