Reactive angioendotheliomatosis or intravascular histiocytosis? An immunohistochemical and ultrastructural study in two cases of intravascular histiocytic cell proliferation.

Two elderly women with complex medical histories presented with erythematous patches, in one case involving the face and forearms, and in the other both elbows. Punch biopsies from both patients revealed intravascular proliferations of medium-sized and large cells with luminal occlusion typical of angioendotheliomatosis. Immunostaining did not show either lymphocytic or endothelial cell antigens but was consistent with a histiocytic differentiation of the intravascular cells in both cases, and was further substantiated by ultrastructural examination in one case. One patient received a course of cyclophosphamide therapy over 15 days. Skin lesions faded but did not disappear. The patient died 10 months later from cardiac and renal failure, which was most probably unrelated to the skin lesions. In the other case, lesions diminished but did not entirely resolve with treatment with low doses of oral prednisone. Angioendotheliomatosis can be divided into a malignant variant, which is an angiotropic lymphoma mostly of B-cell phenotype, and a benign, reactive variant, which is characterized by a proliferation of cells expressing endothelial cell markers. Only one case of angioendotheliomatosis with cells of histiocytic differentiation has been published previously under the name of intravascular histiocytosis. Our cases are very similar to the latter. The question arises as to whether intravascular histiocytic cell proliferation is a neoplastic proliferation of histiocytes or an early stage of classic reactive angioendotheliomatosis representing the residual cells associated with organization of microthrombi, which will be later followed by endothelial cell proliferation.