[Hyperviscosity syndrome].

Hyperviscosity syndrome is a life-threatening complication. Clinical manifestations include neurological impairment, visual disturbance and bleeding. Measurement of plasma or serum viscosity by a viscometer assesses the diagnosis. Funduscopic examination is a key exam because abnormalities are well-correlated with abnormal plasma viscosity. Etiologies are various but symptomatic hyperviscosity is more common in Waldenström's macroglobulinemia and multiple myeloma. Prompt treatment is needed: treatment of the underlying disease should be considered, but generally not sufficient. Symptomatic measures aim to not exacerbate blood viscosity while urgent plasmapheresis effectively reduces the paraprotein concentration and relieves symptoms.