From the Guidelines
Isolated monocytosis should be thoroughly evaluated to determine the underlying cause, with management focusing on treating the underlying condition rather than the monocytosis itself. This approach is crucial because isolated monocytosis can be a sign of various conditions, including chronic infections, inflammatory diseases, malignancies, or recovery from bone marrow suppression 1. The definition of isolated monocytosis typically involves a monocyte count greater than 800-1000 cells/μL in adults, without abnormalities in other blood cell lines.
Key Considerations
- Common causes of isolated monocytosis include:
- Chronic infections (e.g., tuberculosis, endocarditis)
- Inflammatory conditions (e.g., inflammatory bowel disease, rheumatoid arthritis)
- Certain malignancies (particularly myeloid neoplasms like chronic myelomonocytic leukemia)
- Recovery from bone marrow suppression
- Initial workup should comprise a complete history and physical examination, focusing on symptoms of infection, inflammation, or malignancy, along with laboratory tests such as a complete blood count with differential, peripheral blood smear, and basic metabolic panel 1.
- If no obvious cause is found and monocytosis persists, especially in older patients or those with concerning features, hematology consultation may be necessary to consider bone marrow evaluation 1.
Diagnostic Criteria
The diagnosis of conditions like chronic myelomonocytic leukemia (CMML) involves specific criteria, including persistent peripheral blood monocytosis (> 1×10^9/L), absence of the Philadelphia chromosome or BCR-ABL1 fusion gene, and less than 20% blasts in the peripheral blood and bone marrow 1. The presence of dysplasia in one or more cell lines, an acquired clonal cytogenetic or molecular genetic abnormality, or persistence of monocytosis for at least 3 months without evidence of other causes can also support the diagnosis.
Management Approach
Given the variety of potential underlying causes, management of isolated monocytosis should prioritize identifying and treating the root cause, rather than solely focusing on the elevated monocyte count 1. This approach ensures that the underlying condition is addressed, potentially resolving the monocytosis and improving patient outcomes in terms of morbidity, mortality, and quality of life.
From the Research
Definition and Diagnosis of Isolated Monocytosis
- Isolated monocytosis refers to an increase in monocyte count in the blood, which can be caused by various neoplastic and non-neoplastic conditions 2, 3, 4, 5.
- The diagnosis of isolated monocytosis involves the integration of laboratory data, morphology, clinical findings, and the judicious use of ancillary studies 5.
- Flow cytometry studies can help distinguish chronic myelomonocytic leukemia (CMML) from other reactive or neoplastic causes of monocytosis 2.
Differential Diagnosis of Isolated Monocytosis
- The differential diagnosis of isolated monocytosis includes CMML, myeloproliferative neoplasms (MPN), myelodysplastic syndromes (MDS), acute leukemia, and reactive monocytosis 3, 4.
- Molecular investigations and elimination of any reactive cause of monocytosis are necessary to differentiate between these entities 3.
- Histological, immunohistochemical, and phenotypic flow cytometric studies may be useful in evaluating difficult cases 3.
Risk of Haematological Malignancies in Isolated Monocytosis
- Isolated monocytosis is associated with an increased risk of haematological malignancies, including CMML, MPN, and MDS 6.
- The risk of CMML is significantly increased in patients with sustained monocytosis (at least two requisitions in 3 months) 6.
- However, the absolute risk of haematological malignancy associated with isolated monocytosis is low, and haematological malignancy should mainly be suspected when monocytosis is sustained or the clinical presentation raises suspicion of malignancy 6.