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DEFINITION

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  • Pancytopenia with markedly hypocellular marrow and normal marrow cell cytogenetics.

  • Incidence worldwide is 2 to 5 cases/million population per year and 5 to 12 cases/million population per year in the United States (and in other industrialized countries). Incidence is approximately twice as high in Asian countries.

  • Peak incidence between ages 15 and 25 and 65 to 69 years.

  • The definitions for range of severity of aplastic anemia are shown in Table 3–1.

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Table Graphic Jump Location
Table 3–1Degree of Severity of Acquired Aplastic Anemia
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ETIOLOGY AND PATHOGENESIS

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Pathogenesis

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  • Immune suppression of marrow by autoreactive T lymphocytes.

  • Toxic injury to stem and/or progenitor cells (e.g., certain chemotherapy or drugs) (see Table 3–2).

  • Inherited intrinsic stem cell defect (e.g., Fanconi anemia).

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Table Graphic Jump Location
TABLE 3–2SOME DRUGS ASSOCIATED WITH MODERATE RISK OF APLASTIC ANEMIA*
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Etiologic Classification

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Acquired
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  • Acquired T lymphocyte mediated autoimmune suppression of hematopoietic stem cells and/or progenitor cells in most cases (~70%).

  • Paroxysmal nocturnal hemoglobinuria (PNH) (frequently associated with hypoplastic marrow).

  • Chemicals, e.g., benzene. Rare today in countries with workplace regulations limiting exposure.

  • Drugs, e.g., chloramphenicol (see Table 3–2 for most frequent offenders; see also ...

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