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DEFINITION

  • Aplastic anemia is marked by pancytopenia with markedly hypocellular marrow and normal marrow cell cytogenetics.

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

  • Peak incidences are between ages 15 and 25 and 65 and 69 years.

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

TABLE 3–1DEGREE OF SEVERITY OF ACQUIRED APLASTIC ANEMIAa

ETIOLOGY AND PATHOGENESIS

Pathogenesis

  • Immune suppression of marrow by autoreactive T lymphocytes

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

  • Inherited intrinsic stem cell defect (eg, Fanconi anemia)

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TABLE 3–2 SOME DRUGS ASSOCIATED WITH MODERATE RISK OF APLASTIC ANEMIAa
Acetazolamide
Carbamazepine
Chloramphenicol
Gold salts
Hydantoins
Oxyphenbutazone
Penicillamine
Phenylbutazone
Quinacrine

aDrugs with 30 or more reported cases.

Acquired

  • Acquired T lymphocyte–mediated autoimmune suppression of hematopoietic stem cells and/or progenitor cells in most cases (~70%) (Table 3–3)

  • Paroxysmal nocturnal hemoglobinuria (PNH) (may be manifest ...

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