Tuesday, October 30, 2012

Sickle cell crisis case study

Case A 25-year-old African American man is admitted to your service with the diagnosis of a sickle cell pain episode. He was admitted to the hospital six times last year with the same diagnosis, and he was last discharged 2 months ago. Again he presented to the emergency room complaining of abdominal and bilateral lower extremity pain, his usual sites of pain. When you examine him, you note he is febrile to 101°F, respiratory rate 25 breaths per minute, normal blood pressure, and slight tachycardia of 100 bpm. Lung examination reveals bronchial breath sounds and egophony in the right lung base. His oxygen saturation on 2 L/min nasal cannula is 92%. Besides the usual abdominal and leg pain, he is now complaining of chest pain, which is worse on inspiration. Although he is tender on palpation of his extremities, the remainder of his examination is normal. His laboratory examinations reveal elevated white blood cell and reticulocyte counts, and a hemoglobin and hematocrit that are slightly lower than baseline. Sickle and target cells are seen on the peripheral smear

What is the most likely diagnosis?

What is your next step?

What are the potential complications of this condition

ANSWERS

Summary: A 25-year-old African American man with a history of numerous pain crises is admitted for abdominal and bilateral lower extremity pain. He is febrile to 101°F, respiratory rate 25 breaths per minute, and slight tachycardia of 100 bpm. Lung examination reveals bronchial breath sounds and egophony in the right lung base. His oxygen saturation on 2 L/min nasal cannula is 92%. He is now complaining of chest pain, which is worse on inspiration. He has a leukocytosis, an elevated reticulocyte count, and a hemoglobin and hematocrit that are slightly lower than baseline. Sickle and target cells are seen on the peripheral smear.

Most likely diagnosis:Acute chest syndrome.

Next step:Chest radiograph and empiric antibiotic therapy.

Potential complications:Respiratory failure, possible death

ANALYSIS

DEFINITIONS

SICKLE CELL ANEMIA:A congenital defect in hemoglobin formation such that both genes code for hemoglobin S, leading to hemolysis and an abnormal shape of the red blood cell. Affected individuals have numerous complications including pain crises.

ACUTE CHEST SYNDROME:A condition found in individuals with sickle cell disease characterized by fever, tachycardia, chest pain, leukocytosis, and pulmonary infiltrates

CLINICAL APPROACH

Pathophysiology

The molecular structure of a normal hemoglobin molecule consists of two alpha-globin chains and two beta-globin chains. Sickle cell anemia is an autosomal recessive disorder resulting from a substitution of valine for glutamine in the sixth amino acid position of the beta-globin chain. This substitution results in an alteration of the quaternary structure of the hemoglobin molecule. Individuals in whom only half of their beta chains are affected are heterozygous, a state referred to as sickle cell trait.When both beta chains are affected, the patient is homozygous and has sickle cell anemia. In patients with sickle cell disease, the altered quaternary structure of the hemoglobin molecule causes polymerization of the molecules under conditions of deoxygenation. These rigid polymers distort the red blood cell into a sickle shape, which is characteristic of the disease. Sicklingis promoted by hypoxia, acidosis, dehydration, or variations in body temperature.

Complications of Sickle Cell Disease

Acute painful episodes, also known as pain crisis,are a consequence of microvascular occlusion of bones by sickled cells. The most common sites are the long bones of the arms, legs, vertebral column, and sternum. Acute painful episodes are precipitated by infection, cold exposure, dehydration, venous stasis, or acidosis. They usually last 2 to 7 days.

Infectionsare another complication. Patients with sickle cell disease are at greater risk for infections, especially with encapsulated bacterial organisms. Autoinfarction of the spleenoccurs during early childhood secondary to microvascular obstruction by sickled red blood cells. The spleen gradually regresses in size and by age 4 years is no longer palpable. As a consequence of infarction and fibrosis, the immunologic capacity of the spleen is diminished. Patients with sickle cell disease are at greater risk for pneumonia, sepsis, and meningitis by encapsulated organisms such as Streptococcus pneumoniaand Haemophilus influenza.For the same reason, patients with sickle cell disease are at greater risk for osteomyelitis with Salmonellaspp. Acute chest syndromeis a vasoocclusive crisis within the lungs and is associated with infection or pulmonary infarction. Patients with acute chest syndrome present with hypoxia, dyspnea, fever, chest pain, and progressive pulmonary infiltrateson radiography. These episodes may be precipitated by pneumonia causing sickling in the infected lung segments, or, in the absence of infection, intrapulmonary sickling can occur as a primary event. It is virtually impossible to clinically distinguish whether or not infection is present; thus, empiric antibiotic therapy is used.

Aplastic crisisoccurs secondary to viral suppression of red blood cell precursors, most often by parvovirus B19. It occurs because of the very short half-life of sickled red blood cells and consequent need for brisk erythropoiesis. If red blood cell production is inhibited, even for a short time, profound anemia may result. The process is acute and usually reversible, with spontaneous recovery

Other complications of sickle cell disease include hemorrhagic or ischemic stroke as a result of thrombosis, pigmented gallstones, papillary necrosis of the kidney, priapism, and congestive heart failure.

Treatment

The mainstay of treatment of pain crisis is hydration and pain control with nonsteroidal anti-inflammatory agents and narcotics. It is important to also provide adequate oxygenation to reduce sickling. One must search diligently for any underlying infection, and antibiotics are often used empirically when infection is suspected. Acute chest syndromeis treated with oxygen, analgesia, and antibiotics. Sometimes exchange transfusions are necessary. In general, blood transfusions may be required for aplastic crisis, for severe hypoxia in acute chest syndrome, or to decrease viscosity and cerebral thrombosis in patients with stroke. Transfusion does not shorten the duration of pain crisis. To protect against encapsulated organisms, all patients with sickle cell disease should receive penicillin prophylaxisand a vaccination against pneumococcus. Hydroxyureais often used to reduce the occurrence of painful crisis by stimulating hemoglobin F production and thus decreasing hemoglobin S concentration, and should be considered in patients who have repeated episodes of acute chest syndrome, or frequent severe pain crises. The antineoplastic agent 5-deoxyazacytidine (decitabine) may also elevate levels of hemoglobin F without excessive side effects.

QUESTIONS Q 1. Which of the following therapies would most likely decrease the number of sickle cell crises?

A.Hydroxyurea

B.Folate supplementation

C.Prophylactic penicillin

D.Pneumococcal vaccination

ANSWER. A

Q. the syndrome to which it is commonly associated in persons with sickle cell anemia

Salmonella species = osteomylitis

Parvovirus B19 = Aplastic crisis

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