Hairy cell leukemia responsive to anti-thymocyte globulin used as immunosuppressive therapy for aplastic anemia

Hairy cell leukemia (HCL) is occasionally misdiagnosed as aplastic anemia when only a few leukemic cells are present in the circulation. Here, we describe a patient with HCL who initially presented with pancytopenia and received a diagnosis of aplastic anemia. The patient was treated with immunosuppressive therapy including cyclosporine A and anti-thymocyte globulin (ATG). No blood cell transfusion was required for approximately 3 years after ATG therapy. She was referred to our hospital because of an abdominal mass and requiring periodic blood transfusions. A bone marrow biopsy at this time revealed proliferation of lymphocytes with a fried egg appearance and an increase in reticulin fibers that are typical findings of HCL. It is notable that our patient with a presumably long history of HCL and an increase in marrow reticulin fibers showed good recovery of hematopoiesis after cladribine therapy. Some HCL patients may receive an initial diagnosis of aplastic anemia and may show a good response to ATG masking the underlying HCL.