Malignant histiocytosis associated with autoimmune thrombocytopenia.

We describe a patient with malignant histiocytosis whose serum contained an autoantibody against platelet protein. The patient was admitted because of nasal bleeding and high-grade fever. The clinical course was fulminantly progressive and terminated with cerebral hemorrhage. Bone marrow aspirate showed the proliferation of large atypical cells, some of which exhibited phagocytic activity. At postmortem examination, there was diffuse infiltration of these atypical cells in the liver, spleen, kidney, and bone marrow. Morphological, cytochemical, immunohistochemical, and genotypic characteristics suggested that the proliferating cells were derived from the monocyte-macrophage system. Western blot analysis revealed the presence of autoantibody against an approximately 88 kd molecule of platelet proteins. Although the relationship of cause and effect remains to be clarified, this autoantibody appeared to have stimulated thrombophagocytosis of the neoplastic cells.