Myelodysplastic syndrome (MDS) in childhood is a rare hematologic malignancy and its classification has been the subject of some controversy. Cases of pediatric MDS are subdivided into those with features of adult-type MDS and those with myeloproliferative features occasionally observed in infancy and early childhood. There appears to be an international consensus to rename the disease juvenile myelomonocytic leukemia (JMML), which includes all leukemias of childhood previously classed as chronic myelomonocytic leukemia (CMML), juvenile myelomonocytic leukemia(JCML), and infantile monosomy 7 syndrome. We experienced a 6-month-old female infant with JMML who developed extensive extramedullary hematopoiesis. The patient developed abdominal distention, hepatosplenomegaly, anemia, thrombocytopenia, and leukocytosis with significant monocytosis and was found to have a high hemoglobin F level of 30%. Her bone marrow biopsy section and aspirate smears revealed normocellularity with no increment of blast cells and no dysplastic changes. Cytogenetic analysis revealed a normal 46, XX karyotype. Her liver, spleen, lymphnodes, and appendix were found to be heavily infiltrated by partially differentiated myelomonocytic cells. These findings supported the diagnosis of JMML with extensive extramedullary hematopoiesis.

Keywords: Juvenile myelomonocytic leukemia, Childhood myelodysplastic syndrome, Fetal hemoglobin, Infant, Extramedullary hematopoiesis,