Appearance of membranocystic lesion (Nasu)-like changes in Behçet's syndrome. An electron microscopic study of erythema nodosum-like lesions.

Membranocystic lesion (Nasu)-like changes were seen in the subcutaneous fat tissues of erythema nodosum-like lesions in three of 18 patients with Behçet's syndrome. The membranocystic structures, which were derived from degenerative fat cells with a loss of the cell membrane, were observed in the edematous connective tissues accompanied by fibrin deposition and diapedesis of erythrocytes. Electron microscopic evaluation revealed two different patterns of peculiar membranous structures in the cytoplasm of the degenerative fat cells. One was proliferating membrane structures such as well developed Golgi-endoplasmic reticulum, and the other was minute tubular structures such as intracytoplasmic microvesicles. These degenerative fat cells are considered to be derived from abnormal fat cells which lack a cell membrane, but whose cellular and nuclear configurations appear to be normal morphologically, because the cytoplasm of these abnormal cells showed the same tubular structures as those seen in the characteristic architecture of membranocystic lesion-like change. The relation between the appearance of such abnormal cells and the pathologic conditions of erythema nodosum-like lesions in Behçet's syndrome was discussed.