Malignant histiocytosis with eosinophilia

A case of malignant histiocytosis (MH) with persistent eosinophilia, cutaneous involvement, and osteolytic lesions in a 22-year-old male was studied by serial biopsies, hematologic investigations, and finally, necropsy. Original biopsies of skin and bone revealed polymorphous cellular infiltrates composed of histiocytes, eosinophils, lymphocytes, and plasma cells. Although these infiltrates resembled those of histiocytosis X (HX), diagnosis of MH, rather than HX with subsequent “malignant transformation,” was suggested in retrospect by: (1) excessive histiocytic atypia with conspicuous mitotic activity, and, (2) localization of cutaneous infiltrates around appendages and blood vessels in the reticular dermis, with sparing of the papillary zone of the dermis and epidermis. Remission achieved with intensive combination chemotherapy was later followed by development of essentially monomorphous histiocytic malignancy, and terminally, histiocytic leukemia. Rod-shaped structures consistent with Langerhans' cell granules (LCG) were detected in the cytoplasm of atypical histiocytes by electron microscopic study of formalin-fixed autopsy tissue. The presence of LCG in the histiocytes in this case raises the possibility that some examples of MH could represent proliferation of the same cell type that occurs in HX.