Relationship of lysozyme (muramidase) to histiocytic differentiation in malignant histocytosis: an immunohistochemical study.

Malignant histiocytosis (MH) is a rare, usually fatal systemic disease considered to be a neoplasm of true histiocytes. Because MH may be difficult to differentiate from non-Hodgkin's lymphomas or carcinoma, we examined surgical and autopsy material from 10 patients with MH using the immunoperoxidase technique to determine if the presence of intracellular lysozyme is helpful in making this distinction. The cases of MH were divided into three groups based on the degree of cytologic atypia and the amount of phagocytic activity of the neoplastic cells: group I--minimal cytologic atypia and rare erythrophagocytosis; group II--minimal cytologic atypia with extensive erythrophagocytosis: group III--moderate to marked cytologic atypia and rare phagocytosis. Moderate to strong staining for lysozyme was observed in the neoplastic cells of group I, weak or absent staining in group II cells, and no staining in group III cells. These findings suggest the loss of detectable enzyme in poorly differentiated or dedifferentiated neoplastic histiocytes. Consideration must be given to these observations in evaluating the use of lysozyme as a possible serum or tissue aid to the diagnosis of MH.