Aplastic anemias

Aplastic, or hypoplastic, anemias result from injury to or destruction of stem cells in bone marrow or the bone marrow matrix, causing pancytopenia (anemia, granulocytopenia, and thrombocytopenia) and bone marrow hypoplasia. Although commonly used interchangeably with other terms for bone marrow failure, aplastic anemias properly refer to pancytopenia resulting from the decreased functional capacity of a hypoplastic, fatty bone marrow. These disorders generally produce fatal bleeding or infection, particularly when they’re idiopathic or stem from chloramphenicol or from infectious hepatitis. Mortality for aplastic anemias with severe pancytopenia is 80% to 90%.

Causes and incidence

Aplastic anemias usually develop when damaged or destroyed stem cells inhibit red blood cell (RBC) production. Less commonly, they develop when damaged bone marrow microvasculature creates an unfavorable environment for cell growth and maturation. About one-half of such anemias result from drugs (antibiotics and anticonvulsants), toxic agents (such as benzene and chloramphenicol), or radiation. The rest may result from immunologic factors (unconfirmed), severe disease (especially hepatitis), or preleukemic and neoplastic infiltration of bone marrow.

Idiopathic anemias may be congenital. Two such forms of aplastic anemia have been identified: Congenital hypoplastic anemia (Blackfan-Diamond anemia) develops between ages 2 and 3 months; Fanconi’s syndrome, between birth and age 10. In Fanconi’s syndrome, chromosomal abnormalities are usually associated with multiple congenital anomalies, such as dwarfism, and hypoplasia of the kidneys and spleen. In the absence of a consistent familial or genetic history of aplastic anemia, researchers suspect that these congenital abnormalities result from an induced change in the fetus’development.

Incidence is 0.6 to 6.1 cases per 1 million people. There is no racial predilection.

Signs and symptoms

Clinical features of aplastic anemias vary with the severity of pancytopenia but develop insidiously in many cases. Anemic symptoms include progressive weakness and fatigue, shortness of breath, headache, pallor and, ultimately, tachycardia and heart failure. Thrombocytopenia leads to ecchymosis, petechiae, and hemorrhage, especially from the mucous membranes (nose, gums, rectum, and vagina) or into the retina or central nervous system. Neutropenia may lead to infection (fever, oral and rectal ulcers, and sore throat) but without characteristic inflammation.

Diagnosis

Confirmation of aplastic anemia requires a series of laboratory tests:

❑ RBCs are usually normochromic and normocytic (although macrocytosis [larger-than-normal erythrocytes] and anisocytosis [excessive variation in erythrocyte size] may exist), with a total count of 1 million/µl or less. Absolute reticulocyte count is very low.

❑ Serum iron level is elevated (unless bleeding occurs), but total iron-binding capacity is normal or slightly reduced. Hemosiderin (a derivative of hemoglobin [Hb]) is present, and tissue iron storage is visible microscopically.

❑ Platelet, neutrophil, and white blood cell counts fall.

❑ Coagulation tests (bleeding time), reflecting decreased platelet count, are abnormal.

❑ Bone marrow aspiration from several sites may yield a “dry tap,” and biopsy will show severely hypocellular or aplastic marrow, with varied amounts of fat, fibrous tissue, or gelatinous replacement; absence of tagged iron (because iron is deposited in the liver rather than bone marrow) and megakaryocytes (platelet precursors); and depression of erythroid elements.

Differential diagnosis must rule out paroxysmal nocturnal hemoglobinuria and other diseases in which pancytopenia is common.

Treatment

Effective treatment must eliminate any identifiable cause and provide vigorous supportive measures, such as packed RBC, platelet, and experimental histocompatibility locus antigen-matched leukocyte transfusions. Even after elimination of the cause, recovery can take months. Bone marrow transplantation is the treatment of choice for anemia due to severe aplasia and for patients who need constant RBC transfusions. (See Bone marrow transplantation.)

Patients with low leukocyte counts need special measures to prevent infection. The infection itself may require specific antibiotics; however, these aren’t given prophylactically because they tend to encourage resistant strains of organisms. Patients with low Hb levels may need respiratory support with oxygen in addition to blood transfusions.

For older patients, or for those who don’t have a matched bone marrow donor, antithymocyte globulin (ATG) is an alternative treatment. ATG is a horse serum that contains antibodies against human T cells. It may be used in an attempt to suppress the body’s immune system, allowing the bone marrow to resume its blood cell-generating function. Other immunosuppressant agents, such as cyclosporine, may also be used.

Other treatments may include corticosteroids to stimulate erythroid production, marrow-stimulating agents such as androgens (which remain controversial), and colony stimulation factors to encourage growth of specific cellular components.

Special considerations

❑ If the platelet count is low (less than 20,000/µl), prevent bleeding by avoiding I.M. injections, suggesting the use of an electric razor and a soft toothbrush, humidifying oxygen to prevent drying of mucous membranes, avoiding enemas and rectal temperatures, and promoting regular bowel movements through the use of a stool softener and a proper diet to prevent constipation. Also, apply pressure to venipuncture sites until bleeding stops. Detect bleeding early by checking for blood in urine and stool, and assessing skin for petechiae.

❑ Take safety precautions to prevent falls that could lead to prolonged bleeding or hemorrhage.

❑ Help prevent infection by washing your hands thoroughly before entering the patient’s room, by making sure he’s receiving a nutritious diet (high in vitamins and proteins) to improve his resistance, and by encouraging meticulous mouth and perianal care.

❑ Watch for life-threatening hemorrhage, infection, adverse effects of drug therapy, or blood transfusion reaction. Make sure routine throat, urine, nose, rectal, and blood cultures are done regularly and correctly to check for infection. Teach the patient to recognize signs of infection, and tell him to report them immediately.

❑ If the patient has a low Hb level, which causes fatigue, schedule frequent rest periods. Administer oxygen therapy as needed. If blood transfusions are necessary, assess for a transfusion reaction by checking the patient’s temperature and watching for the development of other signs and symptoms, such as rash, hives, itching, back pain, restlessness, and shaking chills.

❑ Reassure and support the patient and his family by explaining the disease and its treatment, particularly if he has recurring acute episodes. Explain the purpose of all prescribed drugs and discuss possible adverse effects, including which ones he should report promptly. Encourage the patient who doesn’t require hospitalization to continue his normal lifestyle, with appropriate restrictions (such as regular rest periods), until remission occurs.

❑ To prevent aplastic anemia, monitor blood studies carefully in the patient receiving anemia-inducing drugs.

❑ Support efforts to educate the public about the hazards of toxic agents. Tell parents to keep toxic agents out of the reach of children. Encourage people who work with radiation to wear protective clothing and a radiation-detecting badge, and to observe plant safety precautions. Those who work with benzene (solvent) should know that 10 parts per million is the highest safe environmental level and that a delayed reaction to benzene may develop.

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Book Source Details

• Book Title: Professional Guide to Diseases (Eighth Edition)
• Author(s): Springhouse
• Year of Publication: 2005
• Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.

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