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Current Peds-Chapter 30: Sickle Cell Disease
Terms in this set (17)
Sickle Cell Disease-Essentials of diagnosis and typical features:
--Neonatal screening test usually with hemoglobins FS, FSC, or FSA (S > A).
--Predominantly African, Mediterranean, Middle Eastern, Indian, or Caribbean ancestry.
--Anemia, elevated reticulocyte count, usually jaundice.
--Recurrent episodes of musculoskeletal or abdominal pain.
--Often hepatomegaly and splenomegaly that resolves.
--Increased risk of bacterial sepsis.
Sickle Cell Disease-General Considerations:
--encompasses a family of disorders with manifestations secondary to the propensity of deoxygenated sickle hgb (S) to polymerize.
--Polymerization of sickle hgb distorts erythrocyte morphology; decreases red cell deformability; causes a marked reduction in red cell life span; increases blood viscosity; and predisposes to inflammation, coagulation activation, and episodes of vaso-occlusion.
--Sickle cell anemia, the most severe sickling disorder, is caused by homozygosity for the sickle gene and is the most common form of sickle cell disease.
--Other clinically important sickling disorders are compound deterozygous conditions in which the sickle gene interacts with genes for hemoglobins C, D (punjab), O (arab), C (harlem), or beta thalassemia.
--Overall, SCD occurs in about 1 of every 400 African-American infants.
--8% of African-Americans are heterozygous carriers of the sickle gene and are said to have sickle cell trait.
Sickle Cell Disease-Signs and symptoms:
--S/S are related to the hemolytic anemia, tissue ischemia, and organ dysfunction caused by vaso-occlusion.
--Most severe in children with sickle cell anemia or sickle beta-thalassemia.
--Physical findings are normal at birth, and symptoms are unusual before 3-4 months of age because high levels of fetal hemoglobin inhibit sickling.
--A moderately severe hemolytic anemia may be present by age 1. This causes pallor, fatigue, and jaundice, and predisposes to the development of gallstones during childhood and adolescence.
--Intense congestion of the spleen with sickled cells may cause splenomegaly in early childhood and results in functional asplenia as early as 3 months of age in sickle cell anemia. This increases risk for overwhelming infection with encapsulated bacteria, particularly pneumococci.
--Up to 30% of pt's experience 1 or more episodes of acute splenic sequestration, characterized by sudden enlargement of the spleen with pooling of red cells, acute exacerbation of anemia, and, in severe cases, shock and death.
--Acute exacerbation of anemia also occurs with aplastic crises, usually caused by infection with human parvovirus & other viruses.
--Recurrent episodes of vaso-occulsion and tissue ischemia cause acute and chronic problems.
--Dactylitis, or hand-and-foot syndrome, is the most common initial symptom of the disease and occurs in up to 50% of children with sickle cell anemia before age 3.
--Recurrent episodes of abdominal and musculoskeletal pain may occur throughout life.
--Overt strokes occur in about 11% of children with SCD and tend to be recurrent. Recurrence is significantly reduced with chronic red cell transfusions.
--Acute chest syndrome: characterized by fever, pleuritic chest pain, and acute pulmonary infiltrates with hypoxemia, is caused by pulmonary infection, infarction, or fat embolism from ischemic bone marrow.
--All tissues are susceptible to damage from vaso-occulsion, and multiple organ dysfunction is common by adulthood in those with sickle cell anemia or sickle beta-thalassemia.
Common Clinical Manifestations of Sickle Cell Disease (SCD):
Children: bacterial sepsis or meningitis; splenic sequestration; aplastic crisis; vaso-occlusive events; dactylitis (sausage digit is inflammation of an entire digit [a finger or toe],and can be painful); bone infarction; acute chest syndrome; stroke; priapism.
Adults: bacterial sepsis; aplastic crisis; vaso-occlusive events; bone infarction; acute chest syndrome; stroke; priapism; acute multi-organ failure syndrome.
Children: functional asplenia; delayed growth and development; avascular necrosis of the hip; hyposthenuria (excretion of urine of low specific gravity due to an inability of the tubules of the kidneys to produce concentrated urine); and cholelithiasis.
Adult: leg ulcers; proliferative retinopathy; avascular necrosis of the hip; cholecystitis; chronic organ failure-liver, lung, kidney; decreased fertility.
Sickle Cell Disease-Laboratory findings:
--Children with sickle cell anemia generally show a baseline Hgb of 7-10 g/dL. This may fall to life-threatening levels at the time of a splenic sequestration or aplastic crisis.
--Baseline reticulocyte count is markedly elevated.
--The anemia is usually normocytic or macrocytic, and the peripheral blood smear typically shows the characteristic sickle cells as well as numerous target cells.
--Pt's with beta-thalassemia also generally have a low MCV and hypochromia. Also tend to have less hemolysis and anemia.
--Pt's with sickle hemoglobin C disease have a fewer sickle forms and more target cells, and the Hgb level may be normal or only slightly decreased because the rate of hemolysis is much less than sickle cell anemia.
--Most infants with sickle hemoglobinopathies born in the US are identified by neonatal testing. Results indicative of possible SCD require prompt confirmation with hemoglobin electrophoresis.
--Children with sickle cell anemia and sickle beta-thalassemia have only Hgb's S, F, and A2. Persons with beta-thalassemia have a preponderance of Hgb S with a lesser amount of hemoglobin A and elevated A2.
--Pt's with sickle hemoglobin C disease have equal amounts of hgb's S and C.
--The use of solubility tests to screen for the presence of sickle hgb should be avoided because a negative result is frequently encountered in infants with sickle cell disease, and a positive result in an older kid does not differentiate sickle cell trait from sickle cell disease. Do not identify hemoglobin variants other than S.
--Hemoglobin electrophoresis is always necessary to accurately identify a sickle disorder.
Sickle Cell Disease-Differential diagnosis:
--It is critical to determine whether the child with only F and S hemoglobins on newborn screening has sickle cell anemia, sickle beta-thalassemia, or is a compound heterozygote for sickle hemoglobin and pancellular hereditary persistence of fetal hemoglobin.
--Such children, when older, typically have 30% fetal hemoglobin and 70% hemoglobin S, and are well.
Sickle Cell Disease-Complications:
--Repeated tissue ischemia and infarction causes damages to virtually every organ system.
--Pt's who require multiple transfusions are at risk of developing transfusion related hemosiderosis and infections as well as red cel alloantibodies.
Sickle Cell Disease-Treatment:
--The cornerstone of treatment is enrollment in a program involving pt and family education, comprehensive outpatient care, and appropriate treatment for acute complications. Important to the success of the program are pscychosocial services, blood bank services, and ready availability of baseline pt information in the setting in which acute illnesses are evaluated and treated.
--Managment of sickle cell anemia and sickle beta-thalassemia includes daily prophylactic penicillin, which should be initiated by age 2 months and continued until at least age 5.
--Pneumococcal conjugate and polysaccharide vaccines should be administered to all children who have SCD. Other routine immunizations, including yearly flu vaccine, should be provided.
--All illnesses associated with fever greater than 38.5 C should be evaluated promptly, bacterial cultures performed, parenteral broad spectrum antibiotics administered, and careful inpatient or outpatient observation conducted.
Sickle Cell Disease-Treatment cont:
--Treatment of painful vaso-occlusive episodes include the maintenance of adequate hydration (avoiding over hydration), correction of acidosis if present, administration of adequate analgesia, maintenance of normal O2 sats, and the treatment of any associated infections.
--Red cell transfusions play an important role in management. Transfusions are indicated to improve O2-carrying capacity during acute severe exacerbations of anemia, as occurs during episodes of splenic sequestration or aplastic crisis.
--Transfusions are not indicated for the treatment of chronic steady-state anemia, which is usually tolerated well, or for uncomplicated episodes of vaso-occlusive pain.
--Simple or partial exchange transfusion to reduce the % of circulating sickle cells is indicated for some severe acute vaso-occlusive events and may be lifesaving. These events include stroke, moderate to severe acute chest syndrome, and acute life-threatening failure of other organs.
--Some pt's with severe complications may benefit from chronic transfusion therapy. The most common indications for transfusions are stroke or an abnormal transcranial doppler assessment indicating an increased risk for stroke. Extended matching for red cell antigents reduces the incidence of alloimmunization.
Sickle Cell Disease-stem cell transplantation?
--Successful stem cell transplant cures sickle cell disease, but to date it's use has been limited due to the risks associated with the procedure, the inability to predict in young children the severity of future complications, and the paucity of HLA-identical sibling donors.
Sickle Cell Disease-oral medications:
--Daily administration of oral hydroxyurea increases levels of fetal hemoglobin, decreases hemolysis, and reduces episodes of pain and dactylitis in young children with sickle cell anemia.
--There is some evidence for a reduction in acute chest syndrome, hospitalization rates, and transfusions with oral hydroxyurea.
--The hematologic effects and short-term toxicity of hydroxyurea in children are similar to those in adults.
--Hydroxyurea is being increasingly prescribed for children and adolescents with sickle cell anemia and sickle beta-thalassemia.
Sickle Cell Disease-prognosis:
--Early identification of neonatal screening of infants with sickle cell disease, combined with comprehensive care that includes prescription of prophylactic penicillin, instruction of splenic palpation, and education on the need to urgently seek care when fever occurs, has decreased mortality in childhood.
--Most pt's now live well into adulthood, but eventually succumb to complications.
Sickle Cell Trait:
--Individuals who are heterozygous for the sickle cell gene have sickle cell trait.
--Neonates are identified by screening that shows hemoglobin FAS (A > S). Accurate identification of older persons with sickle cell trait depends on hemoglobin electrophoresis, which typically shows about 60% hemoglobin A and 40% hemoglobin S.
--No anemia or hemolysis is present. Physical exam is normal. People with sickle cell trait are generally healthy with normal life expectancy.
Sickle Cell Trait--problems associated:
--Sickle trait erythrocytes are capable of sickling, with acedemia and hypoxemia. Thus, the kidneys may be affected with the most common manifestation of sickle trait being hyposthenuria (excretion of urine of low specific gravity due to an inability of the tubules of the kidneys to produce concentrated urine).
--Painless hematuria, normally microscopic, affects about 4% of individuals with sickle cell trait and does not progress to significant renal dysfunction.
--Fewer than 40 individuals have been reported with an exceedingly rare malignancy, renal medullary carcinoma, and all but one have had sickle cell trait.
--Incidence of bacteriuria and pyelonephritis may be increased during pregnancy, but overall rates of maternal and infant morbidity and mortality are not affected by sickle cell trait.
Sickle Cell Trait-activity:
--Exertion at moderate altitudes rarely precipitates splenic infarction.
--In general, exercise tolerance seems to be normal; the incidence of sickle cell trait in black professional football players is similar to that of the general African American population.
--Whether or not the risk of sudden unexplained death during strenuous exercise, as occurs during military basic training, is increased in men with sickle cell trait is controversial.
--Sickle cell trait is most significant for its genetic implications.
--There is no reason to restrict strenuous activity for individuals with sickle cell trait. As with all persons, it is important to be conditioned, dress appropriately, have access to fluids, rest periodically, and perform moderate activity in extreme heat and humidity.
Hemoglobin C disorders:
--Detected by neonatal screening.
--2% of African Americans are heterozygous for hemoglobin C and are said the have hemoglobin C trait.
--Some individuals have no symptoms, anemia, or hemolysis, but the peripheral blood smear may show some target cells.
--Identification of persons with hemoglobin C trait is important for genetic counseling, particularly with regard to the possibility of hemoglobin C disease in offspring.
--Persons with homozygous hemoglobin C have mild microcytic hemolytic anemia and may develop splenomegaly. Peripheral blood smear shows prominent target cells.
--As with other hemolytic anemias, complications of homozygous hemoglobin C include gallstones and aplastic crises.
Hemoglobin E disorders:
--second most common hemoglobin variant worldwide, with a gene frequency up to 60% in northeast Thailand and Cambodia.
--Persons heterozygous for hemoglobin E show hemoglobin FAE by neonatal screening and are asymptomatic and usually not anemic, but they may develop mild microcytosis.
--Persons homozygous for hemoglobin E are also asymptomatic but they may have mild anemia; the peripheral blood smear shows microcytosis and some target cells.
--Compound heterozygotes for hemoglobin E and beta-thalassemia are normal at birth, and like infants with homozygous E, show hemoglobin FE on neonatal screening.
--Unlike homozygotes, they subsequently develop mild to severe microcytic hypochromic anemia. They may exhibit jaundice, hepatosplenomegaly, and poor growth if the disorder is not recognized and treated appropriately. In some cases, the anemia becomes severe enough to require life long transfusion therapy.
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