Chronic Neutrophilic Leukemia with Monocytosis
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Chronic neutrophilic leukemia is a very rare disease with diagnosis based on persistent leucocytosis more than 25×103/l and monocytes less than 1×103/l. The revised WHO criteria 2016 included CSF3R gene mutations as a diagnostic finding.

A 77-year-old man was found to have asymptomatic persistent mature neutrophilic leucocytosis with monocytosis. Molecular study confirmed the presence of a CSF3R gene mutation in the absence of morphological or genetic features of myelodysplasia or other forms of myelodysplastic syndrome.

The patient’s medical history was significant for coronary artery disease, hypertension, chronic obstructive pulmonary disease, bilateral cystic bronchiectasis, moderate pulmonary hypertension, tuberculosis treated 27 years previously, hypothyroidism, and a thyroid nodule. He had hepatosplenomegaly but no lymphadenopathy, and no other malignancy was seen on computed tomography (CT) scanning. At the time of evaluation, he was free of symptoms and had no evidence of infection or drug-induced leucocytosis.

The patient was referred to an oncology center and treated with hydroxyurea and subsequently azacitidine. However, he developed pancytopenia with bone marrow aplasia. He died of neutropenic sepsis. The presence of persistent monocytosis, in this case, created a diagnostic dilemma as to whether the disease was a variant of chronic neutrophilic leukemia or was reactive monocytosis.

The presence of a CSF3R gene mutation is diagnostic for chronic neutrophilic leukemia (CNL).

The monocytosis in this patient might have been a new variant of chronic neutrophilic leukemia.