Hyperviscosity syndrome (HVS) is a condition where the blood thickens so much that it doesnt flow freely through the blood vessels. It is a group of symptoms triggered by an increase in the viscosity of the blood. The increased serum viscosity usually results from increased circulating serum immunoglobulins and can be seen in diseases such as Waldenström macroglobulinemia and multiple myeloma. HVS can also result from increased cellular blood components (typically white or red blood cells) in hyperproliferative states such as the leukemias, polycythemia, and the myeloproliferative disorders.

The clinical presentation in HVS consists principally of the triad of mucosal bleeding, visual changes, and neurologic symptoms. Constitutional symptoms and cardiorespiratory symptoms may also occur. The diagnosis of HVS is confirmed by measurement of elevated serum viscosity in a patient with characteristic clinical manifestations of HVS. There is no exact diagnostic cut-off for serum viscosity, as different patients will have symptoms at different values.

HVS is associated most commonly with plasma cell dyscrasias (the paraproteinemias) and is due to the large size of the excess immunoglobulin M (IgM) paraproteins in these disorders. Waldenström macroglobulinemia is the most common cause and accounts for about 85% of cases of HVS. Less frequently, HVS can occur in multiple myeloma (especially with myeloma proteins of the IgA and IgG3 types) and connective tissue diseases.

The treatment of HVS depends on the underlying cause and the severity of the symptoms. Management consists of supportive care with intravenous fluids, plasmapheresis, and treatment of the underlying hematological condition. HVS is an oncological emergency, and timely treatment can prevent life-threatening complications such as thromboembolic events, myocardial infarction, and catastrophic ischemia that result in multiple organ failure.