hyperviscosity

Hyperviscosity refers to an abnormal increase in blood or plasma viscosity that impairs microcirculatory flow and tissue perfusion. It most often arises in disorders with markedly elevated serum proteins or hematocrit, and can present as a clinical syndrome called hyperviscosity syndrome.

Common causes include Waldenström macroglobulinemia with IgM monoclonal protein, other monoclonal gammopathies with high IgM or non-IgM paraproteins, cryoglobulinemia, multiple myeloma with high IgA/IgG, polycythemia vera, severe dehydration, and sepsis.

Pathophysiology: Increased plasma viscosity raises resistance to flow, particularly in small vessels, leading to sluggish venous return and reduced capillary perfusion. Immunoglobulins or other proteins promote red blood cell aggregation and margination, further hindering microcirculation. The result is organ hypoperfusion and symptoms that may be irreversible if not treated promptly.

Clinical features: Visual disturbances such as blurred vision or retinal hemorrhages, headaches, dizziness, and vertigo; mucosal bleeding; neurologic symptoms including confusion or stroke; congestive heart failure in severe cases; diminished distal pulses or ischemic pain in rare settings.

Diagnosis: Suspect hyperviscosity in patients with compatible symptoms and a high plasma protein or hematocrit. Blood viscosity measurement can aid, but treatment decisions often rely on Ig levels and serum protein electrophoresis with immunofixation. Other tests include complete blood count, hydration status, and evaluation for underlying gammopathy.

Management: Emergent plasmapheresis is the primary treatment for symptomatic hyperviscosity to rapidly reduce viscosity, followed by targeted therapy for the underlying disorder (e.g., chemotherapy for Waldenström macroglobulinemia or myeloma). Supportive care includes IV fluids and management of complications; correction of dehydration or polycythemia is important to prevent recurrence.