Sideroblastic anemia is a microcytic-hypochromic anemia that encompasses a group of heterogenous disorders that have a common defect – failure to use iron in hemoglobin synthesis, despite having enough available in storage.
The chief defect is the sequestration of iron complexes in the mitochondria of erythroblasts, transforming the erythroblasts into sideroblasts.
This anemia may be hereditary or acquired. The acquired form can be either primary or secondary, that is, secondary to ingestion of, or exposure to, such toxins as alcohol and lead, or to such drugs as isoniazid and chloramphenicol. It can also occur as a complication of such other diseases as rheumatoid arthritis, lupus erythematosus, multiple myeloma, tuberculosis, and severe infections. Correction of the secondary acquired form depends on the cause, and generally subsides after the causative drug or toxin is removed or the underlying condition is adequately treated.
The primary acquired form, known as refractory anemia with ringed sideroblasts, is most common in the elderly who are less likely to improve quickly and are more likely to develop serious complications. This idiopathic form is often associated with thrombocytopenia or leukopenia as part of a myelodysplastic syndrome (spinal cord defect).
Effective measures for some patients with the primary acquired form include high doses of androgens or carefully cross-matched transfusions to provide needed hemoglobin, but it generally resists treatment. It usually proves fatal within ten years after onset of complications or an accompanying (concomitant) disease, usually acute leukemia or from respiratory or cardiac complications.
Hereditary sideroblastic anemia is associated with increased gastrointestinal absorption of iron, causing signs of hemosiderosis (a general increase in tissue iron stores without the associated tissue damage) and appears to be transmitted by X-linked inheritance.
This form of anemia occurs mostly in young males; but females are the carriers, who usually show no signs of the disorder. This form usually responds after several weeks of treatment with high doses of pyridoxine (vitamin B6). Folic acid (B9) supplements may also be beneficial when concomitant megaloblastic nuclear changes in RBC precursors are present.
Iron supplements are never given.
In sideroblastic anemia, normoblasts fail to utilize iron to synthesize hemoglobin. As a result, iron is deposited in the mitochondria of normoblasts, which are then termed “ringed sideroblasts”.
Sideroblastic anemia usually produces nonspecific clinical effects, which may exist for several years before being identified. Such effects include anorexia, fatigue, weakness, dizziness, pale skin and mucous membranes, and occasionally, enlarged lymph nodes.
In addition to the cardiovascular and respiratory manifestations common to all anemias, sideroblastic anemia causes mild-to-moderate enlargement of the liver (heptomegaly) and spleen (splenomegaly). Heart and liver failure may develop from excessive iron accumulation in these organs, causing dyspnea, exertional angina, and slight jaundice. However, other eipthelial manifestations and all neurologic manifestations are absent.
At first, sideroblastic anemia may be mistaken for deficiency of stem cells in the marrow (hypoplastic anemia) of iron deficiency anemia. Bone marrow examination establishes the diagnosis. The marrow is packed with erythrocyte stem cells, and mononuclear phagocytes in the marrow are loaded with iron in the form of hemosiderin.
Presence of sideroblasts (the erythrocyte precursors with a necklace-like ring of iron granules around the nucleus), stained with Prussion blue or alizarin red dye, confirms the diagnosis of sideroblastic anemia.
Unlike iron deficiency anemia, sideroblastic anemia lowers hemoglobin and raises serum iron and transferrin levels. In turn, faulty hemoglobin production raises urobilinogen and bilirubin levels. Platelets and leukocytes remain normal, but occasionally, thrombocytopenia or leukopenia occurs.
Some patients with sideroblastic anemia may benefit from phlebotomy (a vein incision) to prevent hemochromatosis, a disorder of iron metabolism that deposits iron in tissues giving a bronze pigmentation, as well as cirrhosis of the liver and diabetes mellitus.
In fact, it is often referred to as the ‘bronze diabetes’. Phlebotomy steps up the rate of erythropoiesis (red cell formation) and uses up excess iron stores, thus reducing serum and total-body iron levels. Since valuable protein is lost during frequent phlebotomy procedures, a high-protein diet is advocated.