[Persistent neutrophilia occurring after pneumonia: a differential diagnosis of neutrophilia based on the WHO classification].

We experienced a 85-year-old female patient with granulocytosis, which occurred after the bacterial pneumonia. The white blood cell counts remained high between 30,000/microl and 120,000/microl for around one year. As the serum G-CSF level was within the normal range and there were no tumors on CT scan images, the existence of G-CSF-producing solid tumors was unlikely. Bone marrow examination revealed hypercellularity without excess of blasts and hiatus leukemia, accompanied by mild dysplasia in myeloid cells and megakaryocytes. No chromosomal abnormalities in bone marrow samples were seen with G-banding and multi-color FISH methods. Major/minor BCR-ABL fusion genes were negative by RT-PCR. As previously reported by several investigators, we often experience difficulties in distinguishing atypical CML from CNL and CMML. In this report, we discussed how to diagnose the cause of granulocytosis based on a literature review.