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Chapter 3: Aplastic Anemia: Acquired and Inherited

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DEFINITION

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

  • Incidence worldwide is two to five cases/million population per year and five to twelve 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 is 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.

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TABLE 3–1DEGREE OF SEVERITY OF ACQUIRED APLASTIC ANEMIA*
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TABLE 3–1 DEGREE OF SEVERITY OF ACQUIRED APLASTIC ANEMIA*
Diagnostic Categories Hemoglobin Reticulocyte Concentration Neutrophil Count Platelet Count Marrow Biopsy Comments
Moderately severe < 100 g/L < 40 × 109/L < 1.5 × 109/L < 50 × 109/L Marked decrease of hematopoietic cells At the time of diagnosis at least two of three blood counts should meet these criteria.
Severe < 90 g/L < 30.0 × 109/L < 0.5 × 109/L < 30.0 × 109/L Marked decrease or absence of hematopoietic cells Search for a histocompatible sibling should be made if age permits.
Very severe < 80 g/L < 20.0 × 109/L < 0.2 × 109/L < 20.0 × 109/L Marked decrease or absence of hematopoietic cells Search for a histocompatible sibling should be made if age permits.

*These values are approximations and must be considered in the context of an individual patient’s situation. (In some clinical trials, the blood count thresholds for moderately severe aplastic anemia are higher [eg, platelet count < 100 × 109/L and absolute reticulocyte count < 60,000 × 109/L].) The marrow biopsy may contain the usual number of lymphocytes and plasma cells; “hot spots,” focal areas of erythroid cells, may be seen. No fibrosis, abnormal cells, or malignant cells should be evident in the marrow. Dysmorphic features of blood or marrow cells are not features of acquired aplastic anemia. Ethnic differences in the lower limit of the absolute neutrophil count should be considered. (See Williams Hematology, 9th ed, Chaps. 64 and 65.)

Source: Williams Hematology, 9th ed, Chap. 35, Table 35–1.

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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 (eg, certain chemotherapy or drugs) (see Table 3–2)

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

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

*Drugs with 30 or more reported cases.

Source: Williams Hematology, 9th ed, Chap. 35, Table 35–3.

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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%) (see Table 3–3)

  • Paroxysmal nocturnal hemoglobinuria (PNH) (may be manifest by cytopenias and hypoplastic marrow)

  • Chemicals (eg, high-dose benzene exposure); rare today in countries with workplace and product regulations ...

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