Cutaneous histiocytic proliferations.

The classification of histiocytic proliferations in the skin is confusing, largely due to faulty use of terms such as reticulum-cell sarcoma and reticulosis. Immunohistochemical staining procedures and ultrastructural studies have made it possible to differentiate the different cells of the mononuclear phagocyte system. The proliferations discussed here were those of the mononuclear phagocyte system that are associated with characteristic skin manifestations. They include proliferations of monocytes (acute monocytic leukemia), proliferations of tissue macrophages or histiocytes (histiocytic sarcoma and its disseminated form, malignant histiocytosis; familial histiocytoses; and multicentric reticulohistiocytosis), proliferations of Langerhans' cells (histiocytosis X), and proliferations of as yet undefined cells of the mononuclear phagocyte system (sinus histiocytosis with massive lymphadenopathy). Clinical features were presented, and special emphasis was placed on incidence, form, localization, histopathology, and marker profile of the proliferating cells in the skin lesions. The close relationship of the different entities was discussed, as was the importance of immune dysfunction.