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INTRODUCTION

The hypoproliferative anemias are normochromic, normocytic, or macrocytic and are characterized by a low reticulocyte count. Hypoproliferative anemia is also a prominent feature of hematologic diseases that are described as bone marrow failure states; these include aplastic anemia, myelodysplastic syndrome (MDS), pure red cell aplasia (PRCA), and myelophthisis. Anemia in these disorders is often not a solitary or even the major hematologic finding. More frequent in bone marrow failure is pancytopenia: anemia, leukopenia, and thrombocytopenia. Low blood counts in the marrow failure diseases result from deficient hematopoiesis, as distinguished from blood count depression due to peripheral destruction of red cells (hemolytic anemias), platelets (idiopathic thrombocytopenic purpura [ITP] or due to splenomegaly), and granulocytes (as in the immune leukopenias). Marrow damage and dysfunction also may be secondary to infection, inflammation, or cancer.

Hematopoietic failure syndromes are classified by dominant morphologic features of the bone marrow (Table 98-1). Although practical distinction among these syndromes usually is clear, some processes are so closely related that the diagnosis may be complex. Separation between aplastic anemia and hypocellular MDS can be particularly difficult. Further, identification of constitutional genetic risk factors has blurred the distinction between acquired and inherited marrow failure. Patients may seem to suffer from two or three related diseases simultaneously, or one diagnosis may appear to evolve into another. Many of these syndromes share an immune-mediated mechanism of marrow destruction and some element of genomic instability resulting in a higher rate of malignant transformation.

TABLE 98-1Differential Diagnosis of Pancytopenia

It is important that the internist and general practitioner recognize the marrow failure syndromes, as their prognosis may be poor if the patient is untreated; effective therapies are often available but sufficiently complicated in their choice and delivery so as to warrant the care of a hematologist or oncologist. The identification of genes in which pathogenic mutations are etiologic for anemia, leukopenia, and thrombocytopenia, and the commercial availability of assays based on sophisticated DNA sequencing and functional consequences of mutations, should allow precise diagnosis early, by the primary care internist and pediatrician as well as by a specialist.

APLASTIC ANEMIA

DEFINITION

Aplastic anemia is pancytopenia with bone marrow ...

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