Chronic neutrophilic leukemia is a very rare disorder; just over 140 cases are reported but many of these may not fulfil the diagnostic criteria.69 It is characterized by a leucocytosis in excess of 25 X 109/L (lack of eosinophilia, basophilia, and few myeloid precursors), absent bcr/abl, and bone marrow myeloid hyperplasia without prominent blasts. A rarer form of CML bears some morphological similarities for CNL but has a variant bcr/abl (BCRe19/ABLa2). Hepatosplenomegaly may be present and in 20% of the cases an associated neoplasm has been reported. Cytogenetics are normal in the majority (90%). There have been no comprehensive studies of molecular biology. One of the difficulties in making a diagnosis of CNL is in differentiating it from a leukemoid reaction, here clonality may be helpful in females who have normal cytogenetics. As a leukemoid reaction is reported in association with myeloma or monoclonal gammopathy of uncertain significance, it would be wise to exclude these entities.
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