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-midimal cytologic atypia and rare erythrophagocytosis; group 11-minimal cytologic atypia with extensive erythrophagocytosis: group 111-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 I1 cells, and no staining in group 111 cells. These findings suggest the loss of detectable enzyme in poorly differentiated or dedifferentiated neoplastic histiocytes. Consideration must be given to these ohservations in evaluating the use of lysozyme as a possible serum or tissue aid to the diagnosis of MH.
Cancer 45:273-279, 1980. ALIGNANI HISTIOCYTOSIS (MH) (histiocytic med-M ullary reticulosis) is a rare, usually rapidly progressive disease characterized clinically by acute onset, fever, hepatosplenomegaly , mild lymphadenopathy, pancytopenia, and jaundice, and histologically by a systemic proliferation of malignant histiocytes with a distinctive distribution. The histiocytes manifest varying degrees of cellular atypia and phagocytic activity, especially erythrophagocyt~sis.~~~~ Although in most instances the diagnosis of MH can be readily established on the clinical and pathologic findings, in some cases the pattern of distribution, marked cellular atypia and/or relative lack of phagocytic activity may render the differentiation of this disease from other tumors, such as non-Hodgkin's large-cell lymphoma or undifferentiated carcinoma, difficult. Lysozyme (muramidase) is normally a major constituent of histiocytes and granulocyte^,^'^'^^^".'^ and immunohistochemical techniques have been successfully utilized to demonstrate the presence of this enzyme in normal and reactive h i ~t i o c y t e s . ' ~