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Updated: Aug 12 2024

Sickle Cell Anemia

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https://upload.medbullets.com/topic/120227/images/differential for anemia - moises d.jpg
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https://upload.medbullets.com/topic/120227/images/sicklecelllow.jpg
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  • Snapshot
    • A 8-year-old African American boy presents with his mother to urgent care for severe pain in his hands and feet. He reports that he has had on and off pain for as long as he can remember, but this time the pain is unremitting and not responsive to pain medications at home. He had been playing outside in the snow when the pain started. His past medical history includes a blood disorder but his parents cannot remember what this was called, as it was diagnosed in a foreign hospital. On physical exam, he is noted to be pale and he has palpable splenomegaly. A peripheral blood smear shows sickled red blood cells. He is started on intravenous pain medications.
  • Introduction
    • Overview
      • sickle cell anemia is an autosomal recessive disease that results in abnormal hemoglobin characterized by hemoglobin S (HbS), resulting in hemolytic anemia and vaso-occlusion
      • sickle cell disease is an overarching term including sickle cell anemia, as well as patients with a sickle mutation (HbS) and a different mutation in the ß-globin gene (e.g., ß-thalassemia or hemoglobin C disease)
        • homozygosity (HbSS)
          • sickle cell anemia
        • heterozygotes (HbSA)
          • sickle cell trait, usually asymptomatic and may confer some resistance to malaria
          • may have painless hematuria as a result of renal papillary necrosis
        • hemoglobin SC disease (HbSC)
          • HbS and HbC
            • hemoglobin C disease (HbC)
              • point mutation in ß-globin gene where glutamic acid is replaced with lysine
    • Genetics
      • inheritance pattern
        • autosomal recessive
      • mutations
        • chromosome 11
        • ß-globin gene
  • Epidemiology
    • Demographics
      • blacks are most commonly affected
    • Risk factors
      • family history
  • ETIOLOGY
    • Pathogenesis
      • pathophysiology
        • recall that hemoglobin (Hb) is a soluble tetramer composed of 2 α-globins and 2 ß-globins
        • HbS results from point mutation of ß-globin gene that substitutes valine for glutamic acid
          • this makes the hemoglobin tetramer poorly soluble and results in distortion of red blood cells (RBCs) into a sickle shape
          • this form causes vaso-occlusion
        • clinical severity is determined by presence of other Hb mutations
        • sickled RBCs undergoes hemolysis every 17 days (1/7th that of normal RBC lifespan)
          • hemolysis generates reactive oxygen species
        • sickled RBCs have a tendency to aggregate in the microvascular circulation, which can lead to:
          • avascular necrosis of bone
  • Presentation
    • Clinical presentation 
      • acute events
        • anemia
        • vaso-occlusive events
          • acute painful episodes
            • previously called “sickle cell crises”
            • may occur on top of chronic pain
            • triggers include cold temperature, stress, alcohol, and menses
            • dactylitis
              • acute pain in hands and feet particularly common in children
          • acute chest syndrome
          • cerebrovascular accidents
          • myocardial infarction
          • priapism
          • renal infarction
          • splenic infarction
            • by 2-4 years of age, patients have functional asplenia
          • venous thromboembolism
          • infection
            • increased risk of infection with encapsulated organisms such as Streptococcus pneumonia, Neisseria meningitidis, Haemophilus influenza type b, and the Salmonella species
            • S. pneumonia is the most common cause for sepsis and meningitis
            • Salmonella is the most common cause for osteomyelitis
      • chronic events
        • pain
        • hemolytic anemia
          • contributing factors include low erythropoietin concentration (can be due to renal disease) and folate deficiency
        • neurologic deficits
        • stunted growth and development
        • renal disease
          • painless hematuria due to papillary infarcts
          • medication toxicities
          • urinary concentrating defect
    • Physical exam
      • splenomegaly
      • jaundice
      • pallor
      • bone/joint tenderness
  • Imaging
    • Radiographs
      • indications
        • acute chest syndrome
      • findings
        • new pulmonary infiltrate of one or more lung segments
  • Studies
    • Prenatal testing currently not routinely used
    • Newborn screening
      • methodology varies by state but can be detected via high performance liquid chromatography (preferred), tandem mass spectrometry, DNA testing, or isoelectric focusing
    • Serum labs
      • decreased hemoglobin and hematocrit
      • increased reticulocyte count
      • mildly elevated fetal hemoglobin (HbF)
      • normocytic anemia
    • Peripheral blood smear
      • Howell-Jolly bodies
        • nuclear remnants of RBCs that have not been phagocytosed due to functional asplenia
      • sickled cells
  • Differential
    • ß-thalassemia
      • key distinguishing factors
        • microcytic anemia
        • no sickle cells on peripheral blood smear
  • Treatment
    • Lifestyle
      • prophylactic treatments
        • modalities
          • daily folic acid
          • penicillin until 5 years of age
          • pneumococcal vaccine
            • prevents pneumococcal sepsis
    • Medical
      • supportive care
        • indications
          • acute attacks
        • modalities
          • hydration
          • oxygen
          • analgesia
      • exchange transfusion
        • indications
          • acute vaso-occlusive events
      • hydroxyurea
        • indications
          • decreases frequency and severity of attacks
          • increases production of fetal hemoglobin, which has a higher affinity for oxygen
    • Surgical
      • hematopoietic cell transplantation
        • indications the only curative treatment
  • Complications
    • Functional asplenia by an early age
      • at increased risk for encapsulated bacterial infection (e.g., Streptococcus and Salmonella)
      • may result in splenic sequestration of RBCs
    • Aplastic crisis associated with parvovirus B19 infection or splenic sequestration crisis
      • supplement with daily folic acid
    • Chronic lung disease and pulmonary hypertention
      • secondary to acute chest syndrome
    • Renal disease
      • can present as inability to concentrate urine, resulting in frequent urination
    • Retinopathy
      • secondary to retinal artery occlusion
    • Cardiomyopathy
      • left-sided diastolic dysfunction with or without pulmonary hypertension
      • due to pulmonary hypertension, chronic anemia and hypoxemia with increased cardiac output, transfusion overload, and hypertension
    • Cholelithiasis
      • secondary to chronic hemolysis
    • Acute sickle hepatic crisis
      • secondary to occlusion the hepatic sinusoids
      • associated with an increased mortality in the mother and fetus
  • Prognosis
    • Overall survival is reduced
    • Prognosis is better with comprehensive care and clinical monitoring
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