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Chapter 50: Lymphocytosis and Lymphocytopenia

LYMPHOCYTOSIS

Definition

  • In adults, lymphocytosis is defined as an absolute lymphocyte count exceeding 4.0 × 109/L.

  • Normal lymphocyte count in childhood is higher than in adults (mean ~6.0 × 109/L) (see Chap. 6).

  • Table 50–1 lists the causes of primary and reactive lymphocytosis.

  • Examine blood film to determine if there is abnormal prevalence of:

    — Blasts, associated with acute lymphoblastic leukemia (see Chap. 55)

    — Small lymphocytes and smudge cells associated with chronic lymphocytic leukemia (CLL) (see Chap. 56)

    — Large granular lymphocytes associated with large granular lymphocyte leukemia (LGLL) (see Chap. 58)

    — Small cleaved lymphocytes associated with low- or intermediate-grade lymphomas (see Chap. 62)

    — Reactive lymphocytes associated with infectious mononucleosis (see Chap. 53)

  • Flow cytometric immunophenotyping of cell surface markers (CD), serum protein electrophoresis and immunofixation for monoclonal immunoglobulins, studies of T-cell–receptor gene rearrangement, or clonal cytogenetic findings can distinguish monoclonal lymphocytosis (B or T lymphocytic leukemia or lymphoma) from polyclonal (reactive) lymphocytosis.

TABLE 50–1CAUSES OF LYMPHOCYTOSIS
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TABLE 50–1 CAUSES OF LYMPHOCYTOSIS

  1. Primary lymphocytosis

    1. Lymphocytic malignancies

      1. Acute lymphoblastic leukemia (Chap. 55)

      2. Chronic lymphocytic leukemia and related disorders (Chap. 56)

      3. Prolymphoblastic leukemia (Chap. 55)

      4. Hairy cell leukemia (Chap. 57)

      5. Adult T-cell leukemia (Chaps. 55 and 67)

      6. Leukemic phase of B-cell lymphomas (Chaps. 61, 62)

      7. Large granular lymphocytic leukemia (Chaps. 58, 67)

        1. Natural killer (NK) cell leukemia (Chap. 67)

        2. CD8+ T-cell large granular lymphocytic leukemia (Chap. 67)

        3. CD4+ T-cell large granular lymphocytic leukemia (Chap. 67)

        4. γ/δ T-cell large granular lymphocytic leukemia (Chap. 67)

    2. Monoclonal B-cell lymphocytosis (Chap. 56)

    3. Persistent polyclonal B-cell lymphocytosis

  2. Reactive lymphocytosis

    1. Mononucleosis syndromes (Chap. 53)

      1. Epstein-Barr virus

      2. Cytomegalovirus

      3. Human immunodeficiency virus

      4. Herpes simplex virus type II

      5. Rubella virus

      6. Toxoplasma gondii

      7. Adenovirus

      8. Infectious hepatitis virus

      9. Dengue fever virus

      10. Human herpes virus type 6 (HHV-6)

      11. Human herpes virus type 8 (HHV-8)

      12. Varicella-zoster virus

    2. Bordetella pertussis

    3. NK-cell lymphocytosis

    4. Stress lymphocytosis (acute)

      1. Cardiovascular collapse

        1. Acute cardiac failure

        2. Myocardial infarction

      2. Staphylococcal toxic shock syndrome

      3. Drug-induced

      4. Major surgery

      5. Sickle cell crisis

      6. Status epilepticus

      7. Trauma

    5. Hypersensitivity reactions

      1. Insect bite

      2. Drugs

    6. Persistent lymphocytosis (subacute or chronic)

      1. Cancer

      2. Cigarette smoking

      3. Hyposplenism

      4. Chronic infection

        1. Leishmaniasis

        2. Leprosy

        3. Strongyloidiasis

      5. Thymoma

Primary Lymphocytosis

Lymphocytic Malignancies

  • Referred to as lymphoproliferative disorders

  • Neoplastic accumulation of monoclonal B cells, T cells, natural killer (NK) cells, or less fully differentiated cells of the lymphoid lineage

Monoclonal B-Cell Lymphocytosis

  • Defined as the expansion of a monoclonal population of B cells with an absolute B-cell count of less than 5.0 × 109/L in the absence of organomegaly, lymphadenopathy, extramedullary involvement, and cytopenias.

  • Two groups (Table 50–2): ...

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