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Chapter 35: Monocytosis and Monocytopenia

INTRODUCTION

  • Monocytes in the blood are in transit. They function in the tissues, where they mature into macrophages and participate in:

    — Inflammation, including granulomatous reactions, atheroma formation, and tissue repair

    — Immunologic reactions, including delayed hypersensitivity

    — Reactions to neoplasia and allografts

  • The need for macrophages in tissues also can be met by local proliferation of macrophages, not requiring increased transit of blood monocytes.

  • In normal subjects, a mean of 87% of blood monocytes intensely express CD14 (lipopolysaccharide receptor) but not CD16 (Fc receptor) (CD14++/CD16–), the classical subset, designated MO1.

  • A mean of 4% of blood monocytes have weaker expression of CD14 and strongly express CD16 (CD14+CD16++), the intermediate subset, designated MO2.

  • A third monocyte subset, at a mean of 9% of blood monocytes, have weak expression of CD14 and strong expression of CD16 (CD14low/CD16++), the nonclassical subset, designated MO3.

  • Distinctions among monocyte subsets have been validated by gene expression profiling.

  • Older persons have a striking decrease in the proportion of classical CD14++/CD16– monocytes to intermediate CD14+/CD16++ monocytes compared with younger persons.

  • Disorders rarely produce abnormalities of monocytes alone in the absence of other blood cell abnormalities.

NORMAL BLOOD MONOCYTE CONCENTRATION

  • The monocyte count averages 1.0 × 109/L in neonatal life, gradually decreasing to a mean of 0.4 × 109/L in adult life.

  • Monocytosis (in adults) is a count greater than 0.8 × 109/L.

  • Monocytopenia is a count less than 0.2 × 109/L.

HEMATOLOGIC DISORDERS ASSOCIATED WITH MONOCYTOSIS

TABLE 35–1DISORDERS ASSOCIATED WITH MONOCYTOSIS
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TABLE 35–1 DISORDERS ASSOCIATED WITH MONOCYTOSIS

  1. Hematologic Disorders

    1. Myeloid neoplasms

      1. Myelodysplastic syndromes

      2. Primary myelofibrosis

      3. Acute monocytic leukemia

      4. Acute myelomonocytic leukemia

      5. Acute monocytic leukemia with histiocytic features

      6. Acute myeloid dendritic cell leukemia

      7. Chronic myelomonocytic leukemia

      8. Juvenile myelomonocytic leukemia

      9. Chronic myelogenous leukemia (m-BCR–positive type)

      10. Polycythemia vera

      11. Primary myelofibrosis

    2. Chronic neutropenias

    3. Drug-induced neutropenia

    4. Postagranulocytic recovery

    5. Lymphocytic neoplasms

      1. Lymphoma

      2. Hodgkin lymphoma

      3. Myeloma

      4. Macroglobulinemia

      5. T-cell lymphoma

      6. Chronic lymphocytic leukemia

    6. Drug-induced pseudolymphoma

    7. Immune hemolytic anemia

    8. Idiopathic thrombocytopenic purpura

    9. Postsplenectomy state

  2. Inflammatory and Immune Disorders

    1. Connective tissue diseases

      1. Rheumatoid arthritis

      2. Systemic lupus erythematosus

      3. Temporal arteritis

      4. Myositis

      5. Polyarteritis nodosa

      6. Sarcoidosis

    2. Infections

      1. Mycobacterial infections

      2. Subacute bacterial endocarditis

      3. Brucellosis

      4. Dengue hemorrhagic fever

      5. Resolution phase of acute bacterial infections

      6. Syphilis

      7. Cytomegalovirus infection

      8. Varicella-zoster virus

      9. Influenza

  3. Gastrointestinal Disorders

    1. Alcoholic liver disease

    2. Inflammatory bowel disease

    3. Sprue

  4. Nonhematopoietic Malignancies

  5. Exogenous Cytokine Administration

  6. Myocardial Infarction

  7. Cardiac Bypass Surgery

  8. Miscellaneous Conditions

    1. Tetrachloroethane poisoning

    2. Parturition

    3. Glucocorticoid administration

    4. Depression

    5. Thermal injury

    6. Marathon running

    7. Holoprosencephaly

    8. Kawasaki disease

    9. Wiskott-Aldrich syndrome

    10. Hemodialysis

Neoplastic or Clonal Monocytic Proliferations

  • Myelodysplastic syndrome

  • Acute myelogenous leukemia (myelomonocytic or monocytic types)

  • Chronic myelomonocytic leukemia

  • Juvenile myelomonocytic leukemia

  • Unusual type of BCR-ABL (p190)–positive chronic myelogenous leukemia with monocytosis

Reactive (Nonclonal) Monocytic Proliferations

  • Neutropenic states: cyclic neutropenia; ...

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