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Chapter 36: 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.

  • Ninety percent of blood monocytes intensely express CD14 (lipopolysaccharide receptor) but not CD16 and 10 percent have weak expression of CD14 and strongly express CD16.

  • Older persons have a striking decrease in the proportion of CD14+CD16– to 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): >0.8 × 109/L.

  • Monocytopenia: <0.2 × 109/L.

HEMATOLOGIC DISORDERS ASSOCIATED WITH MONOCYTOSIS

TABLE 36–1DISORDERS ASSOCIATED WITH MONOCYTOSIS
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TABLE 36–1 DISORDERS ASSOCIATED WITH MONOCYTOSIS

  1. Hematologic disorders

    1. Myeloid neoplasms

      1. Myelodysplastic states

      2. Acute monocytic leukemia

      3. Acute myelomonocytic leukemia

      4. Acute monocytic leukemia with histiocytic features

      5. Acute myeloid dendritic cell leukemia

      6. Chronic myelomonocytic leukemia

      7. Juvenile myelomonocytic leukemia B. Infections

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

      9. Polycythemia vera

    2. Chronic neutropenias

    3. Drug-induced neutropenia

    4. Postagranulocytic recovery

    5. Lymphocytic neoplasms

      1. B-cell Lymphoma

      2. T-cell Lymphoma

      3. Hodgkin disease

      4. Myeloma

      5. Macroglobulinemia

    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

  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

Source: Williams Hematology, 8th ed, Chap. 71, Table 71–1, p. 1042.

Neoplastic or Clonal Monocytic Proliferations

  • Oligoblastic myelogenous leukemia (refractory leukemia with excess blasts or 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; chronic granulocytopenia of childhood; familial benign neutropenia; infantile genetic agranulocytosis; chronic hypoplastic neutropenia.

  • Drug-induced agranulocytosis (transient monocytosis, especially in the recovery phase).

  • Chlorpromazine toxicity, monocytosis precedes the agranulocytosis.

  • Lymphoma.

  • Hodgkin lymphoma.

  • Postsplenectomy state.

  • Myeloma.

INFLAMMATORY AND IMMUNE DISORDERS ASSOCIATED WITH MONOCYTOSIS

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