CNL is a rare myeloproliferative neoplasm characterized by a consistently elevated neutrophil count, usually over 25 × 109/L with a slight increase in immature cells. The average age of patients diagnosed with CNL is 67. Patients may experience the general MPN symptoms discussed earlier and also often present with hepatosplenomegaly.
Neutrophils account for 80% or more of the WBCs with less than 10% immature granulocytes and less than 1% blasts. Basophils and monocytes are not typically increased. The bone marrow is hypercellular with CNL. However, dysplasia and fibrosis are usually not present.
Cytogenetic laboratory analysis shows very few abnormalities. Those that are found include clonal karyotypic abnormalities such as +8, +9, del (20q) and del (11q). The Philadelphia chromosome is absent, as is the BCR/ABL fusion gene.
CNL is a diagnosis of exclusion when other myeloproliferative disorders and reactive neutrophilia have been excluded.