A 3-year-old boy is brought to the clinic by his father due to fatigue and pallor. The patient was seen in another clinic a week ago for abdominal pain and diarrhea. A medication was prescribed to help slow the diarrhea, which resolved, but the patient has been much less playful over the last day. Temperature is 36.7 C (98 F), blood pressure is 110/70 mm Hg, pulse is 120/min, and respirations are 20/min. Physical examination shows an uncomfortable-appearing child with scleral icterus. Cardiac examination shows mild tachycardia with no murmurs. A few ecchymoses are noted along the upper and lower extremities. There is pitting edema along bilateral lower extremities to the knees. The remainder of the examination is unremarkable. Laboratory results are as follows: Peripheral blood smear results are shown in the image below:
Which of the following is the most likely mechanism of this patient's condition?

Question

A 3-year-old boy is brought to the clinic by his father due to fatigue and pallor.  The patient was seen in another clinic a week ago for abdominal pain and diarrhea.  A medication was prescribed to help slow the diarrhea, which resolved, but the patient has been much less playful over the last day.  Temperature is 36.7 C (98 F), blood pressure is 110/70 mm Hg, pulse is 120/min, and respirations are 20/min.  Physical examination shows an uncomfortable-appearing child with scleral icterus.  Cardiac examination shows mild tachycardia with no murmurs.  A few ecchymoses are noted along the upper and lower extremities.  There is pitting edema along bilateral lower extremities to the knees.  The remainder of the examination is unremarkable.  Laboratory results are as follows:  Peripheral blood smear results are shown in the image below:
 Which of the following is the most likely mechanism of this patient's condition?

Quizplus · Accepted Answer

11ec25c8_d69e_7b53_bc81_0d7762083c38_MD0003_00 This patient has normocytic anemia, thrombocytopenia, and edema following a diarrheal illness, findings that are suggestive of hemolytic uremic syndrome (HUS). HUS most commonly occurs 5-10 days after an acute, often bloody, diarrheal illness caused by a Shiga toxin-producing strain of Escherichia coli (serotype O157:H7). The Shiga toxin induces endothelial damage in renal glomeruli, leading to platelet activation, microthrombi formation, and microangiopathic hemolytic anemia. The mechanical intravascular shearing of red blood cells (RBCs) can result in jaundice or scleral icterus (from elevated indirect bilirubin) as well as schistocytes (ie, fragmented RBCs) on peripheral smear, as seen in this patient. Patients may also have signs of thrombocytopenia (eg, bruising) and acute kidney injury (eg, edema, elevated blood urea nitrogen and creatinine). schistocytes Treatment of HUS is supportive and includes fluid and electrolyte management, blood transfusions, and dialysis. Treatment of the prodromal diarrhea with antibiotics or antimotility agents (eg, loperamide), as in this case, can increase the risk of developing HUS and is not recommended. (Choice A) Autoimmune hemolytic anemia results from antibody-mediated destruction of RBCs and usually presents after a respiratory illness or in the setting of systemic disease (eg, systemic lupus erythematosus). The platelet count is typically normal, and spherocytes are seen on peripheral smear. spherocytes (Choice B) Erythropoietin, a hormone produced by the kidneys and involved in RBC maturation, is decreased in patients with chronic kidney disease. This patient's illness is acute, with scleral icterus indicative of hemolytic anemia. Burr cells (echinocytes) would be seen on peripheral smear. Burr cells (echinocytes) (Choice C) Sickle cell anemia is a hemolytic anemia due to a missense mutation in the beta globin gene. Most patients have painful vasoocclusive crises in early childhood, and peripheral smear demonstrates sickled RBCs. sickled RBCs (Choice D) Deficiency of glucose-6-phosphate dehydrogenase, an enzyme that protects cells against oxidative damage, results in hemolysis after exposure to oxidative stress (eg, fava beans, sulfa drugs, infection). Thrombocytopenia is not associated with this condition, and bite cells are present on peripheral smear. bite cells (Choice F) Disseminated intravascular coagulation results from systemic activation of the coagulation system due to an underlying disorder (eg, sepsis, trauma). It not only presents with thrombocytopenia and anemia but also with prolonged PT and activated PTT, not seen in this patient. Educational objective: Hemolytic uremic syndrome typically occurs in children who have recently recovered from a diarrheal illness and who have acute renal injury, thrombocytopenia, and microangiopathic hemolytic anemia with schistocytes on peripheral smear. References: Haemolytic uraemic syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/28242109)

A 3-Year-Old Boy Is Brought to the Clinic by His