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The hyperviscosity syndrome results from high levels of proteins capable of increasing the serum viscosity. Classically, the syndrome is a result of increased amounts of IgM, as seen in Waldenstrom's macroglobulinemia; however, hyperviscosity has also been described in certain cases of multiple myeloma in which abnormal polymers of IgA, IgG, or kappa light chains are produced [1-4].
Hyperviscosity can lead to impairment in the microcirculation of the central nervous system, possibly resulting in headache, dizziness, vertigo, nystagmus, hearing loss, visual impairment, somnolence, coma and seizures. Other possible findings include mucosal hemorrhage due to reduced platelet function, heart failure, which has been attributed to an expanded plasma volume (see below), renal failure, and sausage-like beading in the retinal veins (picture 1).
The diagnosis is established by measuring serum viscosity with an Ostwald viscosimeter. Normal serum viscosity is between 1.4 and 1.8 (measured as the flow time through the viscometer of the patient's serum divided by that of water or saline). Patients with values between 2 and 4 are only rarely symptomatic, while symptoms occur in most patients with values between 5 and 8 [1]. Values above 10 are invariably associated with symptoms. Corresponding values of IgM are commonly between 4 and 8 g/dL but the correlation with viscosity values is not linear [5]. Total serum protein levels usually exceed 10 g/dL. (See "Recognition of monoclonal proteins", section on 'Serum viscosity' and "Epidemiology, pathogenesis, clinical manifestations and diagnosis of Waldenstrom macroglobulinemia", section on 'Overview' and "Epidemiology, pathogenesis, clinical manifestations and diagnosis of Waldenstrom macroglobulinemia", section on 'Hyperviscosity syndrome'.)
Patients presenting with severe neurologic impairment, such as stupor or coma, should be treated with plasma exchange (plasmapheresis) on an emergency basis [1,5-8]. A reasonable initial prescription would be a one plasma volume exchange (see below), replaced with albumin, repeated daily until symptoms subside or until serum viscosity is normal. (See "Prescription and technique of therapeutic plasma exchange".)
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