Malignant histiocytosis: a cytochemical and electron microscopic study of an unusual case.

A 25-year-old black female presented with lymphadenopathy, fever and anemia of two months duration. The diagnosis of malignant histiocytosis was made on the basis of histiocytic infiltrations in the sinuses of spleen, liver and lymph nodes and by the demonstration of erythrophagocytosis in bone marrow. Following splenectomy, the patient developed a leukemic phase with as many as 50 X 10(9) abnormal histiocytes/l and bone marrow necrosis. This patient was also atypical because of multiple granulomas in liver, spleen and lymph nodes. Cytochemical and immunofluorescent stains confirmed that the abnormal cells were derived from the monocyte-macrophage series. Electron microscopy was used to further characterize this abnormal cell population. The electron microscopic and cytochemical evidence confirms that the malignant cells in malignant histiocytosis are derived from monocytes.