Anaemia of rheumatoid arthritis and iron therapy

Iron sequestration and anemia of inflammation

Anemia of chronic disease, also called anemia of inflammation, is characterized by hypoferremia due to iron sequestration that eventually results in iron-restricted erythropoiesis. During the last decade, the molecular mechanisms of iron sequestration have been found to center on cytokine-stimulated overproduction of the iron-regulatory hormone hepcidin. The inflammatory cytokine interleukin-6 (IL-6) is a particularly prominent inducer of hepcidin, but other cytokines are likely to contribute as well. Hepcidin excess causes the endocytosis and proteolysis of the sole known cellular iron exporter, ferroportin, trapping iron in macrophages and iron-absorbing enterocytes. The supply of iron to hemoglobin synthesis becomes limiting, eventually resulting in anemia. Depending on the details of the underlying disease, other inflammation-related mechanisms may also contribute to anemia.

Molecular pathogenesis of anemia of chronic disease

Most patients suffering from chronic infections, chronic inflammatory diseases, and some malignancies develop a mild to moderate anemia designated anemia of chronic disease or anemia of inflammation. Patients with this anemia have low serum iron, low to normal transferrin, and high to normal serum ferritin concentration. The anemia is caused by increased inflammatory cytokines, especially IL-6, inducing increased production of the iron-regulatory hormone hepcidin by hepatocytes. Hepcidin blocks the release of iron from macrophages, hepatocytes, and enterocytes, causing the characteristic hypoferremia associated with this anemia and iron-deprivation of the developing erythrocytes.

Hematologic manifestations of malignancy

Hematologic dysfunction occurs commonly in patients with malignancy. Over half are anemic, often because of acute or chronic blood loss, marrow involvement by the malignancy, marrow suppressive effects of chemotherapy or radiation therapy, or because of the anemia of chronic disease. Less frequently, anemia may result from red cell aplasia, folate or B12 deficiency, hemolytic processes, or hypersplenism. Occasional patients may become polycythemic because of erythropoietin-producing tumors such as renal adenocarcinomas or cerebellar hemangiomas. Elevation of the white cell count is commonly seen, especially in patients with lung cancer. Monocytosis and thrombocytosis, which may be early signs of an underlying malignancy, are also very common and occur in up to half of patients. Thrombocytopenia is commonly a result of therapy or marrow replacement; a few patients may have a syndrome resembling immune thrombocytopenic purpura. Abnormalities of coagulation are present in many patients, and may lead to superficial or deep venous thromboses, pulmonary emboli, nonbacterial thrombotic endocarditis with arterial emboli, bleeding, or acute disseminated intravascular coagulation. A sound understanding of the potential hematologic complications that can result from the malignant process is essential to the clinician caring for cancer patients.