Sickle cell anemia

A congenital hemolytic anemia that occurs primarily, but not exclusively, in blacks, sickle cell anemia results from a defective hemoglobin (Hb) molecule (Hb S) 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.

Sickle cell anemia is most common in tropical Africans and in people of African descent; about 1 in 10 blacks carries the abnormal gene. If two such carriers have offspring, there is a 1 in 4 (25%) chance that each child will have the disease. Overall, 1 in every 400 to 600 black children has sickle cell anemia.

This disease also occurs in Puerto Rico, Turkey, India, the Middle East, and the Mediterranean, as well as in other populations. The defective Hb gene may have persisted in areas where malaria is endemic because the hetero-zygous sickle cell trait provides resistance to malaria and is actually beneficial.

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

Causes

Sickle cell anemia results from homo-zygous inheritance of the Hb S gene, which causes substitution of the amino acid valine for glutamic acid in the B Hb chain. Heterozygous inheritance of this gene results in sickle cell trait, usually an asymptomatic condition. (See Sickle cell trait, page 774.)

Altered cells

The abnormal Hb S found in RBCs of patients with sickle cell anemia becomes insoluble whenever hypoxia occurs. As a result, these RBCs become rigid, rough, and elongated, forming a crescent, or sickle, shape. Such sickling can produce hemolysis (cell destruction).

In addition, these altered cells tend to pile up in capillaries and smaller blood vessels, making the 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 crisis. Four types of crises can occur: painful, aplastic, acute sequestration, or hemolytic.

Painful crisis

Also called a vaso-occlusive crisis or infarctive crisis, painful crisis is the most common crisis and the hallmark of this disease. It usually appears periodically after age 5.

A painful crisis results from blood vessel obstruction by rigid, tangled sickle cells, which causes tissue anoxia and possible necrosis. It’s characterized by severe abdominal, thoracic, muscular, or bone pain and, possibly, increased jaundice, dark urine, or a low-grade fever.

UNDER STUDY:  In pediatric patients with vaso-occlusive crisis, 1-arginine, a precursor to nitric oxide, has been found to be diminished. In adults, it has been significantly diminished in 50% of patients administered to the emergency department with vaso-occlusive crisis.

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.

After the crisis subsides (in 4 days to several weeks), infection may develop, causing such signs as lethargy, sleepiness, fever, and apathy.

Aplastic crisis

Also called megaloblastic crisis, aplastic 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.

Acute sequestration crisis

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

Hemolytic crisis

Quite rare, hemolytic crisis usually occurs in patients who have glucose-6-phosphate dehydrogenase deficiency with sickle cell anemia. 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.

Indicators of 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; temperature over 104° F (40° C); or a fever of 100° F (37.8° C) that persists for 2 days.

Long-term complications

Sickle cell anemia also causes long-term complications. Typically, such a child is small for his age, and puberty is delayed. (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 with organ infarction, such as retinopathy and nephropathy. Premature death commonly results from infection or repeated occlusion of small blood vessels and consequent infarction or necrosis of major organs. For example, cerebral blood vessel occlusion causes cerebrovascular accident.

Diagnosis

A positive family history and typical clinical features suggest sickle cell anemia. Hb electrophoresis showing Hb S or other hemoglobinopathies can 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 show a low RBC count, elevated white blood cell and platelet counts, decreased erythrocyte sedimentation rate, increased serum iron level, decreased RBC survival, and reticulocytosis. Hb may be low or normal.

During early childhood, palpation may reveal splenomegaly, but as the child grows older, the spleen shrinks.

Treatment

Prophylactic antibiotics are given in certain treatments and at follow-up, even when the patient isn’t in crisis. If the patient’s Hb drops suddenly or if his condition deteriorates rapidly, a transfusion of packed RBCs is needed. Supplementation with folic acid is required because of rapid RBC turnover.

In a sequestration crisis, treatment may include sedation, administration of analgesics, blood transfusion, oxygen administration, and large amounts of oral and I.V. fluids. A good antisickling agent isn’t available yet; the most commonly used drug, sodium cyanate, has many adverse effects.

Partial exchange transfusions may be done in crisis situations. Bone marrow transplants are also successful in treatment.

Special considerations

During a painful crisis:

❑ Apply warm compresses to painful areas, and cover the child with a blanket. (Never use cold compresses; this aggravates the condition.)

❑ Administer an analgesic-antipyretic, such as aspirin or acetaminophen.

❑ Encourage the patient to get plenty of bed rest, and help him into a sitting position. If dehydration or severe pain occurs, hospitalization may be necessary.

❑ Suggest biofeedback techniques, which may be helpful.

❑ If the patient is an adolescent or adult male, warn him that he may have sudden, painful episodes of priapism. Explain that such episodes are common and, if prolonged, can have serious reproductive consequences. Advise the patient to report the occurrence of such episodes.

During remission:

❑ 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.

❑ 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.

❑ Stress the need to increase fluid intake to prevent dehydration resulting from impaired ability to concentrate urine. Tell parents to encourage such a child to drink more fluids, especially in the summer, by offering milk shakes, ice pops, and eggnog.

❑ Encourage normal mental and social development in the child by warning 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 whether 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. (See Coping with sickle cell anemia.)

CLINICAL TIP: Women with sickle cell anemia may be a poor obstetric risk and their use of hormonal contraceptives risky. Refer them for birth control counseling by a gynecologist. If women with sickle cell anemia do become pregnant, they should maintain a balanced diet and may benefit from a folic acid supplement.

CLINICAL TIP: During general anesthesia, make sure the patient has optimal ventilation to prevent hypoxic crisis. Provide a preoperative transfusion of packed RBCs as needed.

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Book Source Details

• Book Title: Handbook of Diseases
• Author(s): Springhouse
• Year of Publication: 2003
• Copyright Details: Handbook of Diseases, Copyright © 2003 Lippincott Williams & Wilkins.

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