Differential Diagnosis

This anemia results from an impaired ability of red blood cell precursors to utilize iron in the formation of heme. These abnormal red cell precursors undergo premature destruction while in the marrow. This abnormality of red cell production manifests as a hypochromic microcytic anemia with an elevated RDW, which results from a dimorphic population of cells. Sideroblastic anemia is characterized by ineffective erythropoiesis (low reticulocyte count), increased reticuloendothelial iron stores, and the presence of ringed sideroblasts on bone marrow examination.

Laboratory abnormalities include the above-mentioned anemia plus the presence of polychromatophilic stippled, targeted red blood cells on the peripheral smear. The serum iron and ferritin levels are elevated. The pathognomonic feature is the presence of ringed sideroblasts when the bone marrow is iron stained and examined. An elevated free erythrocyte protoporphyrin (FEP) level distinguishes acquired siderblastic anemia from congenital sideroblastic anemia (low FEP level).

The abnormality of heme synthesis is not completely understood; however, an intramitochondrial heme synthesis defect or an abnormality of pyridoxine metabolism is suspected. Sideroblastic anemias may be congenital or acquired. Acquired forms of this anemia may be secondary to certain medications or alcohol.

There is no satisfactory treatment for sideroblastic anemia other than to correct the underlying cause. A trial with pyridoxine (100-200 mg/day) may prove effective in some cases, and this form of therapy should be employed in all forms of spontaneously acquired disease. Therapy with pyridoxine should be continued for 3 months before it is considered ineffective. In refractory cases, transfusion therapy may offer symptomatic relief; however, iatrogenic hemochromatosis is a potentially lethal complication.