Malignant histiocytosis presenting as lethal midline granuloma: immunohistological study.

Recent advances in immunology have revealed that the "histiocytic" lymphoma of Rappaport is a proliferation of transformed lymphocytes rather than true histiocytes, and that the malignant cells in malignant histiocytosis (MH) are truly transformed histiocytes. We previously reported cases of MH presenting as lethal midline granuloma (MH-LMG) utilising fresh tissue specimens for the detection of cytological markers in a small number of cases. The results showed the true histiocytic nature of the proliferating cells. In this study, paraffin-embedded specimens from 16 cases with MH-LMG were processed for immunoperoxidase procedures to confirm the true histiocytic nature of the proliferating cells. Five cases with nasal and paranasal lymphomas (ML) were also stained to test the usefulness of immunoperoxidase procedures for distinguishing the MH-LMG from ML. Results were as follows; proliferating cells in MH-LMG were histiocytic in nature, staining positive for lysozyme in MH-LMG in contrast to the negative staining in ML.