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Sideroblastic anemias are a group of disorders in which hemoglobin is insufficiently synthesized, because of defective use of iron (although plasmatic iron levels may be normal or elevated). They are said to be sideroblastic because of the presence of ringed sideroblasts in the blood due to accumulated ferritin in mitochondria. Anemias may be microcytic hypochrome (in thalassemia and hereditary sideroblastic anemias), or macrocytic (in idiopathic acquired sideroblastic anemias). In some cases is has a complex presentation, as in saturnism, in which hemolysis is the main symptom. Plasmatic levels or iron are often increased, sometimes normal. Transferrin saturation coefficient may be high to very high. Plasmatic ferritin is more or less elevated. Sideroblast coloration shows over 10-15% of ringed sideroblasts of every stage of maturation. A variety of etiologies have been identified. Congenital forms may be due to (1) thalassemias, or (2) the very rare inherited sideroblastic anemias transmitted as X-linked recessive traits that may respond to vitamin B6. Acquired forms are either toxic-induced, caused by (1) lead poisoning or saturnism (lead is toxic for mitochondrias and directly hemolytic); (2) alcohol; or (3) isoniazide that causes sideroblastic anemias by vitamin B6 deficiency (vitamin B6 is the choice treatment for these disorders). Acquired forms may also be idiopathic, as in acquired idiopathic sideroblastic anemia (AISA) observed in elderly patients of both sexes. Erythropoiesis is the main impaired function, causing macrocytic anemia with both normo- and hypochrome populations. Leukopenia and more seldom thrombocytopenia may be associated. Bone marrow biopsies show excess erythroblasts and over 10% of ringed sideroblasts while other types of cells are normal. The main complications are transfusional, in particular hemochromatosis. Acute leukemia is an unfrequent and late outcome (<10%). |