[Aggressive natural killer cell leukemia with hemophagocytic lymphohistiocytosis: a case report].

A boy, aged 14 years, was admitted due to recurrent cough and expectoration for more than 1 month, with aggravation and fever for 2 days. After admission, he presented with tachypnea and a significant reduction in transcutaneous oxygen saturation, and emergency chest CT examination showed large patchy exudation and consolidation of both lungs. The boy was given tracheal intubation and invasive mechanical ventilation immediately, and his condition was improved after active symptomatic treatment. On the 10th day of hospitalization, the boy experienced fever again, and the laboratory tests showed positive results for Epstein-Barr virus and Mycoplasma antibody IgM, along with pancytopenia, elevated triglycerides, decreased fibrinogen, and increased levels of ferritin and soluble CD25. The boy was diagnosed with hemophagocytic lymphohistiocytosis. Bone marrow biopsy showed the presence of atypical lymphocytes, and aggressive natural killer cell leukemia was considered according to clinical manifestations and flow cytometry immunophenotype. Therefore, the possibility of hemophagocytic lymphohistiocytosis should be suspected in case of severe infection with pancytopenia and rapid disease progression, and hematological malignancies should also be ruled out. Bone marrow biopsy should be performed as early as possible to make a confirmed diagnosis and perform timely treatment.