Sideroblastic anemias

Sideroblastic anemias are caused by impaired iron utilization and are usually part of myelodysplastic syndrome, manifesting as normocytic-normochromic anemia with a high red blood cell distribution width (RDW) or microcytic-hypochromic anemia with increased levels of serum iron, ferritin, and transferrin saturation.

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Causes sideroblastic anemia

Sideroblastic anemias, among other anemias, are characterized by inadequate utilization of iron for hemoglobin synthesis despite normal or elevated iron levels (iron utilization disorder). Other anemias with impaired iron utilization include some hemoglobinopathies, most notably the thalassemias. Sideroblastic anemias are characterized by the presence of polychromatophilic, granular, target-shaped red blood cells (siderocytes). Sideroblastic anemias are part of myelodysplastic syndrome, but may be congenital or secondary to drugs (chloramphenicol, cycloserine, isoniazid, pyrazinamide) or toxins (including ethanol and lead). There is a deficiency in reticulocyte production, intramedullary death of red blood cells, and bone marrow erythroid hyperplasia (and dysplasia). Although hypochromic RBCs are also produced, other RBCs may be large, resulting in normochromic values, so that RBC size variability (dimorphism) usually corresponds to a high RDW.

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Symptoms sideroblastic anemia

Anemia is common in myelodysplasia. The anemia may be microcytic or normochromic-normocytic, usually with a dimorphic (large and small) cell population. Bone marrow examination shows decreased erythroid activity, megaloblastoid and dysplastic changes, and often an increase in ringed sideroblasts. Anemia due to iron transport deficiency (atransferrinemia) is extremely rare. It occurs when iron cannot be transported from storage sites (eg, liver mucosal cells) to erythropoietic precursors. A possible mechanism is the absence of transferrin or an abnormality of the transferrin molecule. Additional features include hemosiderosis of lymphoid tissue, especially along the gastrointestinal tract.

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Diagnostics sideroblastic anemia

Sideroblastic anemia is suspected in patients with microcytic or high RDW anemia, especially with elevated serum iron, serum ferritin, and transferrin saturation. Peripheral blood smear shows red blood cell dimorphism. Red blood cells may be granular. Bone marrow examination is mandatory and shows erythroid hyperplasia; iron staining reveals iron-bound mitochondria (ringed sideroblasts) in developing red blood cells. Other features of myelodysplasia are often present. Serum lead testing is performed when the cause of sideroblastic anemia is unclear.

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Treatment sideroblastic anemia

Elimination of toxins or medications (and especially cessation of alcohol intake) may restore hematopoiesis. Rarely, congenital abnormalities respond to pyridoxine 50 mg orally 3 times daily, but the response is incomplete.