After studying this chapter you should be able to:
Name the categories of chronic illnesses that are associated with anemia.
Explain the pathogenesis of the anemia of chronic inflammation and the role of hepcidin.
Understand the pathogenesis of the anemia of renal failure.
Summarize the use of recombinant erythropoietin: its efficacy, safety, and clinical applications.
All of the different types of anemia covered in preceding chapters (4-6) as well as those that follow this one (Chapters 8-11) are primary hematologic disorders arising because of an inherited or an acquired defect that directly lowers the red cell mass by impairing erythropoiesis or shortening cell survival. The importance of these -disorders notwithstanding, it is worth stressing that among the most common anemias and the ones most prevalent in patients hospitalized on a medical or pediatric service are those secondary to an underlying chronic illness (summarized in Table 7-1).
ANEMIA OF CHRONIC INFLAMMATION
A chronic systemic inflammatory disorder persisting more than a month is nearly always accompanied by anemia. As indicated in Table 7-1, the chronic inflammation is usually due to infection, tumor, or a connective tissue disorder. A wide array of infections may be responsible, including subacute bacterial endocarditis, tuberculosis, lung abscess, osteomyelitis, and pyelonephritis. In some types of chronic infections, the pathogenesis is more complex. For example, in AIDS the HIV virus can directly infect hematopoietic progenitor cells. In malaria and babesiosis, the parasite infects and destroys circulating red cells.
TABLE 7-1Anemia of Chronic Illness ||Download (.pdf) TABLE 7-1 Anemia of Chronic Illness
Anemia of chronic inflammation
Connective tissue disorders
Anemia of renal insufficiency
Anemia of chronic liver disease
Anemia of endocrine hypofunction
Tumors vary considerably in their ability to trigger an inflammatory response. Some secrete inflammatory cytokines as part of their profiles of aberrant gene expression. In others, impairment of oxygen or nutrient supply to the interior of the tumor can result in necrosis and an inflammatory response. In some tumors, such as the leukemias and lymphomas and those that have metastasized to bone, red cell production is further compromised by marrow invasion.
Anemia is encountered in a wide variety of inflammatory disorders not associated with either infection or cancer. In many of these conditions, autoimmune attack on the patient's cells and tissues is accompanied by a robust inflammatory response. Rheumatoid arthritis is the most prevalent connective tissue disorder and a prototypical cause of anemia of chronic inflammation. Polymyalgia rheumatica/temporal arteritis is associated with even more intense inflammation and accordingly more severe anemia. In anemia due to systemic lupus erythematosus, the deleterious impact of inflammation is often compounded by increased red cell destruction (due to the presence of autoantibodies) and the anemia of renal insufficiency (described in the following section).