Hyperviscosity in plasma cell dyscrasias.

Plasma cell dyscrasias are characterized by a malignant clonal proliferation of plasma cells. Due to the excessive production of abnormal clonal gammaglobulins, or paraproteins, there are major hemorheologic changes in the circulation. As a result, clinical manifestations of the hyperviscosity syndrome become a major cause of morbidity and mortality. Pathogenic factors for the hyperviscosity are due both to increased plasma viscosity and to increased erythrocyte aggregation, leading to increased whole blood viscosity. These changes are dependent on the plasma concentration as well as the molecular size of the paraprotein with the threshold for onset of hyperviscosity for IgG >15 g/dl, for polymerized IgG3 >4-5 g/dl, for IgA >10-11 g/dl; for polymerized IgA >6-7 g/dl and for IgM >3 g/dl. Correspondingly, the incidence of symptomatic hyperviscosity in Waldenstrom's macroglobulinemia is 10-30%, while that in IgG myeloma is 2-6%. Clinically, the syndrome has neurologic features of headache and dizziness, visual changes, renal failure, and cardiac failure from increased plasma volume. Thrombotic complications are frequent. Paradoxically, there can be bleeding complications due to impairment of platelet function. Removal of the paraprotein by plasma exchange (plasmapheresis) can effectively reduce the hyperviscosity. Long-term control of paraprotein production can be achieved by chemotherapy. The early recognition of the symptoms of hyperviscosity, confirmed by laboratory findings of increased paraproteins and of increased blood viscosity, is essential for the proper management of this group of disorders.