Chronic myelomonocytic leukemia in childhood.

A four-year-old child with recurrent infections and increasing hepatosplenomegaly over a three-year period was evaluated. Increased numbers of myeloid precursors packed the bone marrow and infiltrated the peripheral blood. A diagnosis of chronic myelogenous leukemia (CML) was considered but could not be confirmed by laboratory studies appropriate for the types of CML usually observed in childhood. Examination of the patient's peripheral blood smears revealed many atypical monocytoid cells with unipolar hairy projections. Scanning electron microscopy showed these to be leukemic monoblasts with characteristic broad-based ruffles on the cell surface. A population of myeloid precursors possessing narrow ridge-like profiles was also observed. Progressive infiltration of the spleen caused hypersplenism which necessitated splenectomy. Subsequently, massive liver and bone marrow involvement led to the patient's death. Terminally, the proliferating blast cells were demonstrated to be leukemic monoblasts by analysis of cytochemical staining patterns, surface immunoglobulins, serum lysozyme levels, and monocyte-mediated antibody-dependent cellular cytotoxicity studies. The findings in this case are most compatible with a diagnosis of chronic myelomonocytic leukemia (CMML), a condition not previously described in childhood. Several myeloproliferative disorders with prolonged survival have been reported in children, but special studies were not performed to determine which cell lines were abnormally proliferating. The similarities between these children and our patient with CMML suggest that monocyte studies may be useful in the diagnosis of these unusual disorders, provide insights into their pathogenesis, and aid in the selection of appropriate therapy.