A distinct subtype of idiopathic myelofibrosis with bone marrow features mimicking hairy cell leukemia: Evidence of an autoimmune pathogenesis

A young female patient presented with severe anemia and myelofibrosis. The spleen was not enlarged on clinical examination and no leukoerythroblastosis or tear‐drop poikilocytosis was found. A bone marrow biopsy disclosed severe myelofibrosis and many megakaryocytes, which appeared morphologically normal. A striking feature was a heavy spongy infiltration by large lymphocytic cells, which were tartrateresistant acid phosphatase negative and without hairy projections. This bone marrow appearance highly resembled the clear cell appearance of the hairy cell infiltrate in hairy cell leukemia. A diagnosis of acute autoimmune myelofibrosis was made. During high‐dose glucocorticoid therapy the bone marrow fibrosis completely resolved and there was an improvement of peripheral blood values. The disorder is supposed to feature a distinct clinicopathological entity within the syndrome of idiopathic myelofibrosis. The disease should be considered in the differential diagnosis of patients with myelofibrosing disorders, including acute myelofibrosis and hairy cell leukemia.