Malignant histiocytosis with slow clinical course

Previously we reported that malignant histiocytosis presenting as lethal midline granuloma (MH-LMG) showed rapidly progressive course (mean survival 14 months). Because of the same biopsy findings of polymorphic cellular infiltrates (PCI), we considered that MH-LMG and midline malignant reticulosis (MMR) are similar disease. In this paper, we studied 5 cases with MH-LMG showing slow clinical course with more than 5 year survivals, and a similarity found in MH-LMG and MMR in which disseminated and localized disease are present, is discussed. Among clinical data, no abnormality in hematologic findings in MH-LMG with slow clinical course was the only different point from that with progressive course. Biopsy findings of PCI in which atypical histiocytes with positive reactions for lysozyme by immunoperoxidase procedures were present, were identical with those in MH-LMG with progressive course. Autopsy findings justified a diagnosis of MH. MH with slow clinical course seems to be identical with MMR showing localized lesion. Therefore a term MMR should be replaced by a term MH-LMG in the classification of LMG.