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.
TABLE 3–1DEGREE OF SEVERITY OF ACQUIRED APLASTIC ANEMIA* |Favorite Table|Download (.pdf) 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. |
ETIOLOGY AND PATHOGENESIS
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)
TABLE 3–2SOME DRUGS ASSOCIATED WITH MODERATE RISK OF APLASTIC ANEMIA* |Favorite Table|Download (.pdf) TABLE 3–2 SOME DRUGS ASSOCIATED WITH MODERATE RISK OF APLASTIC ANEMIA*
|Gold salts |
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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