Intravascular coagulation: the cause of necrotic arachnidism

Abstract

Venom from the brown recluse spider (Loxosceles reclusa) when injected into the skin of rabbits causes a characteristic inflammatory necrotic ulcer, comparable to the natural necrotic spider bite seen in man. In the rabbit the progressive hemorrhage and painful necrosis of the skin are associated with thrombocytopenia, fibrinogenemia, and prolongation of the clotting time. Ultrastructural studies of rabbit lesions show endothelial damage and thrombosis of blood vessels as early as 3 hr follwoing injection. Disintegration of the endothelial cells, hemorrhage, and thrombosis precede the inflammatory infiltrate and necrosis. It is suggested that damage to blood vessels, activation of the clotting system, and release of local mediators of inflammation account for the characteristic progression of necrotic arachnidism.