Sideroblastic Anemias

Sideroblastic anemia is an umbrella term for a group of heterogenous disorders with a common defect: failure to use iron in hemoglobin synthesis despite the availability of adequate iron stores. As a result, iron is deposited in the mitochondria of normoblasts, and characteristic rings surround the nucleus of this cell.

Sideroblastic anemias can be acquired or hereditary; the acquired form, in turn, can be primary or secondary. In many instances, hereditary sideroblastic anemia responds to treatment with pyridoxine (vitamin B6). Correction of the secondary acquired form depends on the causative disorder; the primary acquired (idiopathic) form resists treatment and usually proves fatal within 10 years after onset of complications or a concomitant disease.

Causes

Hereditary sideroblastic anemia is most prevalent in young males and appears to be transmitted by X-linked inheritance; females are carriers and usually show no signs of this disorder.

The acquired form may be secondary to ingestion of or exposure to toxins, such as alcohol and lead, or to drugs, such as isoniazid and chloramphenicol. It can also occur as a complication of neoplastic and inflammatory diseases, such as lymphoma, rheumatoid arthritis, lupus erythematosus, multiple myeloma, tuberculosis, and severe infections.

The primary acquired form, whose cause is unknown, is most common in elderly people but occasionally develops in young people. It's often associated with thrombocytopenia or leukopenia.

Symptoms

Symptoms of sideroblastic anemia vary depending on the severity of the condition. Sideroblastic anemia may occur without symptoms and be detected only during a medical examination that includes a blood test. When they occur, symptoms may include the following:

• Rapid heartbeat.
• Lightheadedness or dizziness.
• Headache.
• Irritability and other mood disturbances.
• Mental confusion.
• Loss of sexual drive.
• Shortness of breath on exertion.

Diagnostic tests

Blood tests are used to examine the appearance and other characteristics of red cells and to measure the amount of iron in the blood. Bone marrow biopsy is also used.

Treatment

The underlying cause determines the course of treatment. Hereditary sideroblastic anemia usually responds to several weeks of treatment with high doses of pyridoxine.

The acquired secondary form subsides after the causative drug or toxin is removed or the underlying condition is adequately treated. Folic acid supplements may be beneficial when concomitant megaloblastic nuclear changes in RBC precursors are present. Deferoxamine may be used to treat chronic iron overload in selected patients.

Carefully crossmatched transfusions (providing needed hemoglobin) or high doses of androgens are effective palliative measures for some patients with the primary acquired form of sideroblastic anemia. This form is essentially refractory to treatment andusually leads to death from acute leukemia or from respiratory or cardiac complications.

Some patients with sideroblastic anemias may benefit from phlebotomy to prevent hemochromatosis. Phlebotomy increases the rate of erythropoiesis and uses up excess iron stores; thus, it reduces serum and total-body iron levels.

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