Intravascular malignant histiocytosis mimicking central nervous system vasculitis: an immunopathological diagnostic approach.

A 53-year-old man presented with a lumbosacral polyradiculoneuropathy and developed fluctuating encephalopathy suggestive of multifocal small vessel disease. Postmortem examination demonstrated multifocal vascular occlusion by undifferentiated cells confined to the intravascular space. Extravascular spread was found only in spleen and liver. The presence of lysozyme and absence of factor VIII in the cytoplasm of the malignant cells confirmed their histiocytic nature. This patient had an unusual intravascular form of malignant histiocytosis that must be included in the differential diagnosis of multifocal vascular disease.