Malignant histiocytosis: a clinical, histologic, and immunohistochemical study of 20 cases.

To better characterize the diagnostic criteria and clinical behavior of malignant histiocytosis, 20 patients treated at the Mayo Clinic during a 25-year period were studied. A wide spectrum of cytologic differentiation was observed, with cells ranging from bland to highly anaplastic; hemophagocytosis was prominent only in conjunction with a bland histologic appearance. In surgical specimens, the diagnosis of malignant histiocytosis necessitated the use of immunoperoxidase methods for lysozyme, immunoglobulin light chain, and alpha-antitrypsin content, as well as cytochemical stains for acid phosphatase and nonspecific esterase. All autopsies showed that organ involvement had varied somewhat from that reported earlier. The correct diagnosis of malignant histiocytosis was made prior to death in only ten of the 20 cases. The mean survival in the 17 fatal cases was 7.6 months; three of the seven patients treated by aggressive chemotherapy achieved complete remission. Relatively longer survival was correlated with initial confinement to the skin and the absence of cytopenia or liver function abnormalities. Three patients with pulmonary involvement from malignant histiocytosis had apparent inappropriate antidiuretic hormone secretion in the absence of central nervous system disease. The accelerated clinical progression of malignant histiocytosis and its response to current chemotherapeutic regimens make rapid diagnosis and familiarity with the pathologic variations seen in this disorder imperative. Routine utilization of special light-microscopic and immunohistochemical stains is mandatory.