Diseases » Iron deficiency anemia

Sickle cell anemia

Sickle cell anemia: Excerpt from Professional Guide to Diseases (Eighth Edition)

A congenital hemolytic anemia that occurs primarily but not exclusively in blacks, sickle cell anemia results from a defective hemoglobin (Hb) molecule (HbS) that causes red blood cells (RBCs) to roughen and become sickle-shaped. Such cells impair circulation, resulting in chronic ill health (fatigue, dyspnea on exertion, swollen joints), periodic crises, long-term complications, and premature death.

Penicillin prophylaxis can decrease morbidity and mortality from bacterial infections. Half of patients with sickle cell anemia die by their early twenties; few live to middle age.

Causes and incidence

Sickle cell anemia results from homozygous inheritance of the gene that produces HbS (chromosome 11). It's inherited as an autosomal recessive trait. Heterozygous inheritance of this gene results in sickle cell trait, a condition that usually produces no symptoms. (See Sickle cell trait.) Sickle cell anemia is most common in tropical Africans and in people of African descent; about 1 in 10 American blacks carries the abnormal gene. However, sickle cell anemia also appears in other ethnic populations, including people of Mediterranean or East Indian ancestry.

If two parents who are both carriers of sickle cell trait (or another hemoglobinopathy) have offspring, each child has a 25% chance of developing sickle cell anemia. (See Inheritance patterns in sickle cell anemia, page 22.) Overall, 1 in every 400 to 600 black children has sickle cell anemia. The defective HbS-producing gene may have persisted because, in areas where malaria is endemic, the heterozygous sickle cell trait provides resistance to malaria and is actually beneficial.

The abnormal HbS found in such patients' RBCs become insoluble whenever hypoxia occurs. As a result, these RBCs become rigid, rough, and elongated, forming a crescent or sickle shape. (See Comparing normal and sickled red blood cells.) Such sickling can produce hemolysis (cell destruction). In addition, these altered cells tend to pile up in capillaries and smaller blood vessels, making blood more viscous. Normal circulation is impaired, causing pain, tissue infarctions, and swelling. Such blockage causes anoxic changes that lead to further sickling and obstruction.

Signs and symptoms

Characteristically, sickle cell anemia produces tachycardia, cardiomegaly, systolic and diastolic murmurs, pulmonary infarctions (which may result in cor pulmonale), chronic fatigue, unexplained dyspnea or dyspnea on exertion, hepatomegaly, jaundice, pallor, joint swelling, aching bones, chest pains, ischemic leg ulcers (especially around the ankles), and increased susceptibility to infection. Such symptoms usually don't develop until after age 6 months because large amounts of fetal Hb protect infants for the first few months after birth. Low socioeconomic status and related problems, such as poor nutrition and education, may delay diagnosis and supportive treatment.

Infection, stress, dehydration, and conditions that provoke hypoxia — strenuous exercise, high altitude, unpressurized aircraft, cold, and vasoconstrictive drugs —may all provoke periodic crises. A painful crisis (vasoocclusive crisis, infarctive crisis), the most common crisis and the hallmark of the disease, usually appears periodically after age 5. It results from blood vessel obstruction by rigid, tangled sickle cells, which causes tissue anoxia and possible necrosis. This type of crisis is characterized by severe abdominal, thoracic, muscular, or bone pain and possibly worsening jaundice, dark urine, and a low-grade fever.

Autosplenectomy, in which splenic damage and scarring is so extensive that the spleen shrinks and becomes impalpable, occurs in patients with long-term disease. This can lead to increased susceptibility to Streptococcus pneumoniae sepsis, which can be fatal without prompt treatment. Infection may develop after the crisis subsides (in 4 days to several weeks), so watch for lethargy, sleepiness, fever, or apathy.

An aplastic crisis (megaloblastic crisis) results from bone marrow depression and is associated with infection, usually viral. It's characterized by pallor, lethargy, sleepiness, dyspnea, possible coma, markedly decreased bone marrow activity, and RBC hemolysis.

In infants between ages 8 months and 2 years, an acute sequestration crisis may cause sudden massive entrapment of RBCs in the spleen and liver. This rare crisis causes lethargy and pallor and, if untreated, commonly progresses to hypovolemic shock and death.

A hemolytic crisis is quite rare and usually occurs in patients who also have glucose-6-phosphate dehydrogenase deficiency. It probably results from complications of sickle cell anemia, such as infection, rather than from the disorder itself. Hemolytic crisis causes liver congestion and hepatomegaly as a result of degenerative changes. It worsens chronic jaundice, although increased jaundice doesn't always point to a hemolytic crisis.

Suspect any of these crises in a sickle cell anemia patient with pale lips, tongue, palms, or nail beds; lethargy; listlessness; sleepiness with difficulty awakening; irritability; severe pain; a fever over 104° F (40° C); or a fever of 100° F (37.8° C) that persists for 2 days.

Sickle cell anemia also causes long-term complications. Typically, the child is small for his age and has delayed puberty. (However, fertility isn't impaired.) If he reaches adulthood, his body build tends to be spiderlike — narrow shoulders and hips, long extremities, curved spine, barrel chest, and elongated skull. An adult usually has complications from organ infarction, such as retinopathy and nephropathy. Premature death commonly results from infection or from repeated occlusion of small blood vessels and consequent infarction or necrosis of major organs (such as cerebral blood vessel occlusion causing stroke).

Diagnosis

A positive family history and typical clinical features suggest sickle cell anemia. Hb electrophoresis showing HbS or other hemoglobinopathies can also confirm it. Electrophoresis should be done on umbilical cord blood samples at birth to provide sickle cell disease screening for all neonates at risk.

Additional laboratory studies may show a low RBC count, elevated white blood cell and platelet counts, decreased erythrocyte sedimentation rate, increased serum iron, decreased RBC survival, and reticulocytosis. Hb levels may be low or normal. During early childhood, palpation may reveal splenomegaly, but, as the child grows older, the spleen shrinks.

Treatment

Treatment begins before age 4 months with prophylactic penicillin. If the patient's Hb drops suddenly or if his condition deteriorates rapidly, he'll need to be hospitalized for a transfusion of packed RBCs. In a sequestration crisis, treatment may include sedation, administration of analgesics, a blood transfusion, oxygen administration, and large amounts of oral or I.V. fluids.

Daily folic acid supplementation is recommended to prevent megaloblastic crisis. Hydroxyurea, which causes an increase in the synthesis of fetal Hb and a significant reduction in crises, is being used for some patients with sickle cell anemia. Researchers have found it helpful for some patients because it reduces the frequency of painful crises and episodes of acute chest syndrome and decreases the need for blood transfusions.

Newer drugs are being developed to manage sickle cell anemia. Some of these agents try to induce the body to produce more fetal Hb, which helps decrease the amount of sickling. Others work by increasing the binding of oxygen to sickle cells. Currently, bone marrow transplantation offers the only cure for sickle cell anemia. Gene therapy (replacing HbS with normal HbA) may be the ideal treatment, but it's difficult to perform.

Special considerations

Supportive measures during crises and precautions to avoid them are important. Here are some actions you can take during a painful crisis:

❑ Apply warm compresses to painful areas, and cover the child with a blanket. (Never use cold compresses because they aggravate the condition.)

❑ Administer an analgesic-antipyretic, such as aspirin or acetaminophen. (Additional pain relief may be required during an acute crisis.)

❑ Encourage fluids and bed rest, and place the patient in a sitting position. If dehydration or severe pain occurs, hospitalization may be necessary.

❑ When cultures indicate, give antibiotics as ordered.

During remissions:

❑ Advise the patient to avoid tight clothing that restricts circulation.

❑ Warn against strenuous exercise, vasoconstricting medications, cold temperatures (including drinking large amounts of ice water and swimming), unpressurized aircraft, high altitude, and other conditions that provoke hypoxia.

Pediatric tip

Stress the importance of normal childhood immunizations, meticulous wound care, good oral hygiene, regular dental checkups, and a balanced diet as safeguards against infection.

❑ Emphasize the need for prompt treatment of infection.

❑ Inform the patient of the need to increase fluid intake to prevent dehydration due to impaired ability to concentrate urine properly. Tell parents to encourage the child to drink more fluids, especially in the summer, by offering fluids such as milkshakes and ice pops.

During pregnancy or surgery:

❑ Warn women with sickle cell anemia that they may have increased obstetrical risks. However, use of hormonal contraceptives may also be risky; refer them for birth control counseling to a qualified obstetric or gynecologic health care provider.

❑ If such women do become pregnant, they should maintain a balanced diet and may benefit from a folic acid supplement.

❑ During general anesthesia, a patient who has sickle cell anemia requires optimal ventilation to prevent hypoxic crisis. Make sure the surgeon and the anesthesiologist know that the patient has sickle cell anemia. Provide a preoperative transfusion of packed RBCs, as needed.

General tips:

❑ To encourage normal mental and social development, warn parents against being overprotective. Although the child must avoid strenuous exercise, he can enjoy most everyday activities.

❑ Refer parents of children with sickle cell anemia for genetic counseling to answer their questions about the risk to future offspring. Recommend screening of other family members to determine if they're heterozygote carriers. These parents may also need psychological counseling to cope with guilt feelings. In addition, suggest they join an appropriate community support group.

❑ Adolescents or adult males with sickle cell anemia may develop sudden, painful episodes of priapism. Such episodes are common and, if prolonged, can have serious reproductive consequences. Advise the patient to contact the physician when these episodes occur.

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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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More About This Book: Title: Professional Guide to Diseases (Eighth Edition) Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2005 ISBN: 1-58255-370-X

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