Classic hairy cell leukemia with an aggressive presentation.

Hairy cell leukemia is an indolent neoplasm involving mature B cells with distinct cytologic and immunophenotypic features. It typically presents in older adults with pancytopenia and splenomegaly. We describe a patient who presented with severe anemia and thrombocytopenia, leukocytosis, and splenomegaly. He had an unusually complicated clinical course including pancytopenia refractory to multiple transfusions, oropharyngeal bleeding requiring intubation for airway protection, subdural hematoma after minor trauma, and sepsis due to Staphylococcus aureus bacteremia. This case highlights the importance of considering hairy cell leukemia in the differential diagnosis of all patients with cytopenia and splenomegaly, as this is a disease that has excellent response to treatment with purine analogs.