Chronic Myelomonocytic Leukemia with Myelofibrosis Resulting in Sudden Massive Pleural Effusion during Cytoreductive Therapy with Hydroxycarbamide

Pleural effusion may occur as a rare complication associated with myeloid hematological malignancies. However, it occasionally occurs in patients with myelodysplastic/myeloproliferative neoplasms(MDS/MPN), especially in chronic myelomonocytic leukemia(CMML)with marked leukocytosis. Pleural effusion can also develop in hematological disorders with bone marrow fibrosis. Here, we report a case of CMML with bone marrow fibrosis, in which massive pleural effusion developed rapidly during cytoreductive therapy with hydroxycarbamide(HU). At the same time, the patient's leukocytosis was well controlled by the HU treatment. Although the cause of the patient's pleural effusion was unclear, despite a detailed thoracoscopic investigation, it is suspected that the invasion of leukemia cells or extramedullary hematopoiesis in the thoracic cavity may have led to this complication. Our findings suggest that in MPN and hematological disorders with bone marrow fibrosis, pleural effusion should be considered as a possible complication and should be carefully monitored, even when cytoreductive therapy is effective.