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Overview of Plasma Cell Disorders
(Dysproteinemias; Monoclonal Gammopathies; Paraproteinemias; Plasma Cell Dyscrasias)
Plasma cell disorders are a diverse group of disorders of unknown etiology characterized by
(For structural features and classification of the immunoglobulins, see Components of the Immune System : Antibodies.)
After developing in the bone marrow, undifferentiated B cells enter peripheral lymphoid tissues, such as lymph nodes, spleen, and gut (eg, Peyer patches). Here, they begin to differentiate into cells, each of which can respond to a limited number of antigens. After encountering the appropriate antigen, some B cells undergo clonal proliferation into plasma cells. Each clonal plasma cell line is committed to synthesizing one specific immunoglobulin antibody that consists of 2 identical heavy chains (gamma [γ], mu [μ], alpha [α], delta [δ], or epsilon [ε]) and 2 identical light chains (kappa [κ] or lambda [λ]). A slight excess of light chains is normally produced, and urinary excretion of small amounts of free polyclonal light chains (≤ 40 mg/24 h) is normal.
Plasma cell disorders are of unknown etiology and are characterized by the disproportionate proliferation of one clone. The result is a corresponding increase in the serum level of its product, the monoclonal immunoglobulin protein (M-protein). M-proteins may consist of both heavy and light chains or of only one type of chain.
Complications of plasma cell proliferation and M-protein production include the following:
Autoimmune damage of organs (particularly the kidneys): Some M-proteins show antibody activity
Impaired immunity: Decreased production of other immunoglobulins
Bleeding tendency: M-protein may coat platelets, inactivate clotting factors, increase blood viscosity, and cause bleeding by other mechanisms
Secondary amyloidosis: M-protein can be deposited within organs
Osteoporosis, hypercalcemia, anemia, or pancytopenia: Clonal cells can infiltrate bone matrix and/or marrow
Plasma cell disorders can vary from asymptomatic, stable conditions (in which only the protein is present) to progressive cancers (eg, multiple myeloma—for classification, see Classification of Plasma Cell Disorders). Rarely, transient plasma cell disorders occur in patients with drug hypersensitivity (sulfonamide, phenytoin, and penicillin), with presumed viral infections, and after heart or transplant surgery.
Classification of Plasma Cell Disorders
Plasma cell disorders may be suspected because of clinical manifestations, findings during evaluation of anemia, or an incidental finding of elevated serum protein or proteinuria that leads to further evaluation with serum or urine protein electrophoresis. Electrophoresis detects M-protein, which is further evaluated with immunofixation electrophoresis for identification of heavy and light chain classes.
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