[A case of chronic neutrophilic leukemia accompanied with severe bone marrow fibrosis which was effectively treated by hydroxyurea].

A 57-year-old man was admitted to hospital because of leukocytosis. He showed mild splenomegaly and, laboratory studies revealed elevated mature neutrophil count without morphological abnormality, mild anemia and elevated neutrophil alkaline phosphatase score. The serum granulocyte colony stimulating factor concentration was below 30 pg/ml. Bone marrow was a dry tap, and biopsy specimen revealed severe fibrosis. The peripheral blood karyotype was 46, XY with no rearrangement of bcr-abl. The patient was diagnosed as having chronic neutrophilic leukemia (CNL) with bone marrow fibrosis. He was successfully treated with hydroxyurea (HU) 1000 mg/day. The peripheral blood leukocyte was decreased to the normal level and, the bone marrow biopsy specimen changed mild fibrosis. During the follow up period of 11 months, the neutrophil count was well controlled without any side effect. This is a rare case of CNL accompanied with bone marrow fibrosis which was effectively treated by the administration of HU.