Histologic findings in hyperviscosity syndrome: Evidence of a rheologic mechanism of tissue damage

Morphologic features of two cases of hyperviscosity syndrome are shown. They concern both the vessels and the surrounding tissue. The most distinctive features are the engorgement of small vessels by clumps of red cells, which appear often distorted and irregular in shape, and perivascular and pericellular edema. The vessel wall may be thin and normal in appearance at microscopic examination or thickened by a deposition of PAS-positive material. The connection between the impairment of microcirculation and the lesion of the surrounding tissue appears documented by the morphologic findings.