Clinical aspects of malignant histiocytosis and its related disorders in childhood.

Malignant histiocytosis (MH, histiocytic medullary reticulosis, HMR) in children demonstrates following characteristics; (1) Clinical symptoms are mostly due to hypercytokinemia elicited by proliferating T cells and activated monocytes/macrophages, (2) The bone marrow smear is helpful in the diagnosis revealing proliferation of monoblastoid (or immunoblastoid) cells and monocytes/macrophages including hemophagocytes, (3) No cohesive lesions in the involved lymph nodes or spleen, (4) As therapeutic modality anti-neoplastic agents are indispensable, (5) Patients who become refractory to such treatment suffer multiple organ failure and take fatal outcomes, (6) Viral infection may play some roles in the pathogenesis. Our clinical studies on 20 patients indicated that MH (HMR) consists mostly of aberrant T cell proliferative disorders and hyperferritinemia, high serum phenylalanine-tyrosine ratio and hypercytokinemia (elevated levels of serum interferon-gamma, cytotoxic factor and soluble interleukin-2 receptor) are useful indicators reflecting disease activity.