Ultrastructure of endothelial cell necrosis in classical erythema nodosum.

As evidence of vascular involvement in classical erythema nodosum unassociated with Behçet's disease, the occurrence of endothelial cell necrosis based on the development of dark cell degeneration was observed by electron microscopy in the vasculature of the dermis and subcutaneous fat. The incidence of endothelial cell necrosis in all segments of the microcirculatory system was roughly 20% in three of 12 patients. The remaining nine patients showed a very low rate of necrosis, including two patients in whom endothelial cell necrosis was totally absent. The presence of necrotic endothelial cells that are forced out and eliminated by neighboring intact endothelial cells into the vascular lumen is closely associated with thrombus formation in the cutaneous vasculature. The incidence at which endothelial cell necrosis occurs in classical erythema nodosum is not always high; however, it is concluded that endothelial cell necrosis may play a significant role in the pathogenesis of erythema nodosum.