Monocytosis



Monocytosis


Carla S. Wilson, MD, PhD





Key Facts


Terminology



  • Absolute blood monocyte count > 0.8 × 109/L in adults and > 3.5 × 109/L in neonates


Etiology/Pathogenesis



  • Monocytes differentiate into tissue macrophages/histiocytes and dendritic cells


  • Common causes of monocytosis are inflammation, immune-mediated disorders, infections, neoplasms


  • Seen during interruption in neutrophil production


Clinical Issues



  • Enzyme cytochemical stain: Nonspecific esterase(+)


  • IHC: CD68(+), CD68R(+), CD163(+)


  • Flow cytometric analysis: CD4, CD14, CD11b, CD36, CD38, CD64, CD13, CD15, CD33, HLA-DR, & CD45 positive


Microscopic Pathology



  • Monocytes average 12-20 µm in diameter



    • Often indented nucleus with reniform or folded appearance


    • Abundant gray to blue-gray cytoplasm with fine azurophilic granules


    • Reactive features include ↑ cytoplasmic vacuolation


  • Monoblasts and promonocytes are rare in normal bone marrows


  • Increased immature monocytes may be seen during regeneration


Top Differential Diagnoses



  • Chronic myelomonocytic leukemia


  • Acute myeloid leukemia with monocytic differentiation






The monocyte image has a reniform nucleus with slightly clumped chromatin and abundant pale blue cytoplasm. Unlike the metamyelocyte and neutrophil, no secondary cytoplasmic granulation is observed.






Monocytes image are strongly positive for nonspecific esterase stains, including α-naphthyl butyrate esterase, as shown here. In contrast, neutrophils image show negative staining.


TERMINOLOGY


Synonyms



  • Increased monocytes, monocytic hyperplasia


Definitions



  • Absolute blood monocyte count > 0.8 × 109/L in adults and > 3.5 × 109/L in neonates


  • Focus on nonneoplastic monocytoses


ETIOLOGY/PATHOGENESIS


Environmental Exposure



  • Alcoholic liver disease


  • Therapy related



    • Colony stimulating factor (CSF) therapy


    • Glucocorticoid administration


    • Drug-induced neutropenia or hemolytic anemia


    • Exogenous cytokine therapy


    • Postsplenectomy


  • Injury: Thermal injury, marathon running


Infectious Agents



  • Bacteria



    • Tuberculosis, brucellosis, subacute bacterial endocarditis, syphilis, Rocky mountain spotted fever


  • Virus



    • Cytomegalovirus, Epstein-Barr virus, varicella-zoster virus, parvovirus B19


  • Parasite



    • Malaria, visceral leishmaniasis


Inflammatory/Immune-mediated Disorders



  • Collagen vascular diseases



    • Systemic lupus erythematosus, rheumatoid arthritis, polyarteritis nodosa, temporal arteritis, myositis


  • Gastrointestinal disorders



    • Regional enteritis, ulcerative colitis, sprue


  • Liver diseases with increased bone marrow monocytes



    • Autoimmune hepatitis, primary biliary cirrhosis, non-immune-mediated cirrhosis


  • Sarcoidosis


  • Cytopenias



    • Immune-mediated hemolytic anemia


    • Immune-mediated thrombocytopenia


Neoplasms



  • Hematopoietic disorders



    • Lymphoma (Hodgkin and non-Hodgkin), plasma cell myeloma, myelodysplastic syndrome


  • Nonhematopoietic tumors



    • Carcinomas and sarcomas



      • Common finding at diagnosis


    • Prominent monocytosis if M-CSF secreting tumor


Other



  • Cytopenias



    • Hemolytic anemia


    • Chronic or congenital neutropenias



      • Wiskott-Aldrich syndrome


  • Myocardial infarction


General

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Jun 13, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Monocytosis

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