Hyperviscosity as a complication in a variety of disorders.

For a considerable time, hyperviscosity syndrome has been widely recognized as a serious manifestation of polycythemia and plasma cell dyscrasia. In this article a number of conditions will be considered in which the association with hyperviscosity has been more recently recognized and is less widely known. These conditions are hyperleukocytosis, retinoic acid therapy, and connective tissue disease such as rheumatoid arthritis. The essential problems in the first two are the hugely elevated white cell count (WCC) and the mechanical properties of the leukocytes, in other words, their relatively poor deformability and their adhesiveness for the endothelium. In the last, the essential problem is hugely elevated plasma viscosity due to immunocomplexes. They lead to increased flow resistance, especially in the microvessels, abnormal flow, and significant clinical symptoms. The details of the causes of the hyperviscosity, the symptoms that result, and the forms of treatment are discussed.