From the Guidelines
Increased monocytes, or monocytosis, is typically a response to underlying infections, inflammation, or certain diseases, and the most recent evidence suggests that a comprehensive diagnostic workup is necessary to determine the cause, as seen in the 2024 study by Fautrel et al. 1. When evaluating monocytosis, it is essential to consider various potential causes, including:
- Infections such as bacterial, viral, fungal, or parasitic diseases
- Chronic inflammatory conditions like inflammatory bowel disease, rheumatoid arthritis, and lupus
- Certain cancers, particularly leukemias and lymphomas
- Medications, including corticosteroids and certain chemotherapy drugs Monocytes play a crucial role in the immune system, functioning as phagocytes and developing into macrophages and dendritic cells in tissues. The diagnostic workup for suspected chronic myelomonocytic leukemia (CMML) should include patient history, physical examination, complete blood count, peripheral blood smear examination, bone marrow aspiration and biopsy, conventional cytogenetic analysis, and molecular assays, as recommended in the 2013 study by the Haematologica journal 1. In the context of Still's disease, which can also present with monocytosis, the 2024 study by Fautrel et al. 1 highlights the importance of considering alternative diagnoses, such as malignancies, infectious diseases, and other immune-mediated inflammatory diseases, and using biomarkers like IL-18 and S100 proteins to support the diagnosis. Key points to consider in the diagnostic workup of monocytosis include:
- Comprehensive diagnostic criteria, as proposed by the FAB group and the WHO classification
- Patient evaluation at diagnosis, including history, physical examination, and laboratory tests
- Exclusion of reactive causes of monocytosis, such as infectious diseases and solid tumors
- Consideration of alternative diagnoses, such as Still's disease, and the use of biomarkers to support the diagnosis.
From the Research
Reasons for Increased Monocytes
- Monocytosis can be caused by a range of conditions, including chronic myelomonocytic leukemia (CMML) and other hematological malignancies 2
- Infection and inflammation can also lead to an increase in monocytes, as they play a crucial role in the recruitment of monocytes to peripheral tissues 3
- Monocytes are heterogeneous and can display diverse responses to different stimuli, contributing to both pro- and antitumoral immunity in cancer 4
- Sustained monocytosis can further increase the risk of CMML, although the diagnosis is still rare 2
Associated Conditions
- Chronic myelomonocytic leukemia (CMML) is a prototypical neoplasm with monocytosis, and can be distinguished from other reactive or neoplastic causes using flow cytometry studies 5
- Other hematological malignancies, such as leukemia and lymphoma, can also be associated with monocytosis 2
- Inflammatory and degenerative diseases can also contribute to the pathogenesis of monocyte recruitment 3
Diagnostic Approach
- A stepwise diagnostic approach is recommended for patients presenting with monocytosis, including basic studies and flow cytometry analysis 5
- Logistic regression can be used to model the risk of hematological malignancy and death following monocytosis 2
- Monocyte-targeted therapeutic strategies may be effective in treating cancer, highlighting the importance of understanding monocyte heterogeneity and functions in cancer progression 4