Life history of cutaneous vascular lesions in Sneddon's syndrome.

Sneddon's syndrome is a potentially fatal arterio-occlusive disorder characterized by generalized livedo racemosa and cerebrovascular lesions. Skin biopsies often fail to yield diagnostic arterial lesions. In the present series, affected vessels were found in skin biopsies from 12 of 15 patients with Sneddon's syndrome. Selection of the correct biopsy site (seemingly uninvolved skin at the center of a livedo racemosa area), adequate biopsy size (1 to 2 cm), and serial sections are essential for the detection of relevant vascular pathology. Only small to medium-sized arteries of the dermis-subcutis boundary were found to be involved. Lesions follow a distinct course. The initial stage displays partial detachment of endothelial cells, adhesion of mononuclear cells interspersed with fibrin ("endothelitis"), a marked edema of the surrounding connective tissue with numerous dilated capillaries, and a predominantly lymphohistiocytic infiltrate with polymorphonuclear leukocytes. In the early phase a sponge-like plug is formed from mononuclear cells, fibrin, and red blood cells, leading to partial to complete obstruction. A perivascular inflammatory infiltrate, devoid of polymorphonuclear leukocytes, is located around affected arteries; in the adventitia of the occluded vessel, a very regular corona of dilated capillaries appears that is continuous with more peripheral dilated and branching vessels. Organization of the occluding plug ensues in the intermediate stage by "subendothelial cell proliferation," most likely due to immigrating smooth muscle cells. In the final stage, the occluding artery undergoes fibrosis, shrinkage, and atrophy.