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- Hyperviscosity syndrome (HVS) is the clinical consequence of increased blood viscosity.
- The classic clinical symptoms are the triad of mucosal bleeding, visual disturbances, and neurologic signs.
- Viscosity is the resistance a material has to change in form.
- The higher the blood viscosity, the more the internal resistance to blood flows.
- Increased cardiac output is required to provide adequate perfusion of hyperviscous blood.
- Oxygen delivery is impaired as transit through the microcirculatory system slows. This impaired microcirculatory oxygenation gives rise to the clinical symptoms of this syndrome.
- Hyperviscosity occurs when there is elevation of either the cellular or acellular components of circulating blood.
- Acellular (protein) hyperviscosity:
- The most common cause (85–90%) of hyperviscosity is increased concentration of γ globulins:
- Monoclonal gammopathies: From malignant diseases like Waldenstrom macroglobulinemia and multiple myeloma
- Polyclonal gammopathies: Usually rheumatic diseases (very rare)
- Cellular (blood cell) hyperviscosity:
- Much less common (10–15%)
- Increased numbers of RBC, as in polycythemia vera
- Increased concentration (>100,000) of WBC, as in acute and chronic leukemia
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