Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content +++ 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 Graphic Jump LocationTABLE 3–1DEGREE OF SEVERITY OF ACQUIRED APLASTIC ANEMIAaView Table||Download (.pdf) TABLE 3–1 DEGREE OF SEVERITY OF ACQUIRED APLASTIC ANEMIAa 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 × 109/L <0.5 × 109/L <30 × 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 × 109/L <0.2 × 109/L <20 × 109/L Marked decrease or absence of hematopoietic cells Search for a histocompatible sibling should be made if age permits. aThese 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, 10th ed, Chaps. 62 and 63.) +++ 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) ++ Table Graphic Jump Location|Download (.pdf)|Print 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 ... Your Access profile is currently affiliated with [InstitutionA] and is in the process of switching affiliations to [InstitutionB]. Please select how you would like to proceed. Keep the current affiliation with [InstitutionA] and continue with the Access profile sign in process Switch affiliation to [InstitutionB] and continue with the Access profile sign in process Get Free Access Through Your Institution Learn how to see if your library subscribes to McGraw Hill Medical products. Subscribe: Institutional or Individual Sign In Error: Incorrect UserName or Password Username Error: Please enter User Name Password Error: Please enter Password Sign in Forgot Password? Forgot Username? Download the Access App: iOS | Android Sign in via OpenAthens Sign in via Shibboleth You already have access! Please proceed to your institution's subscription. Create a free profile for additional features.