A 7-year-old boy comes to the office for follow-up. A week ago, the patient began having episodes of bloody diarrhea that have since resolved. His current laboratory studies show elevated blood urea nitrogen and serum creatinine levels. Complete blood count reveals anemia and thrombocytopenia. Coagulation studies are within normal limits. His peripheral blood smear is shown in the image below. Which of the following is the most likely cause of this patient's anemia?

Question

A 7-year-old boy comes to the office for follow-up.  A week ago, the patient began having episodes of bloody diarrhea that have since resolved.  His current laboratory studies show elevated blood urea nitrogen and serum creatinine levels.  Complete blood count reveals anemia and thrombocytopenia.  Coagulation studies are within normal limits.  His peripheral blood smear is shown in the image below.  Which of the following is the most likely cause of this patient's anemia?

Quizplus · Accepted Answer

11ec160b_397c_956c_9249_3bbac777c4c9_MD0001_00 The clinical presentation and the peripheral blood smear shown are typical of hemolytic uremic syndrome (HUS). Most cases of childhood HUS are preceded by bloody diarrhea, often caused by Shiga-like toxin released from enterohemorrhagic Escherichia coli (particularly strain O157:H7). Undercooked ground beef is a common cause of HUS. The smear contains classic schistocytes (fragmented red cells) and few platelets. Schistocytes are diagnostic of a traumatic mechanism and indicate either microangiopathic hemolytic anemia (eg, HUS, thrombotic thrombocytopenic purpura [TTP], disseminated intravascular coagulation [DIC]) or mechanical damage (eg, prosthetic valve, severely calcified valves). HUS and TTP lie on a spectrum. Unlike in DIC, the coagulation system is not activated in HUS-TTP; therefore, coagulation studies (prothrombin time and partial thromboplastin time) are normal, as seen with this patient. (Choice A) Autoimmune hemolytic anemia (AIHA) is due to an altered immune response and the production of antibodies against erythrocytes. AIHA can occur following infections with Mycoplasma pneumoniae and Epstein-Barr virus but not usually following a diarrheal illness. In addition, thrombocytopenia and renal failure are not associated with AIHA. (Choice B) Erythropoietin deficiency results in normocytic, normochromic anemia; neither schistocytes nor decreased platelets are present. In addition, erythropoietin deficiency is usually seen in chronic renal failure; this patient has acute renal failure. (Choice C) Glucose-6-phosphate dehydrogenase (G6PD) deficiency causes hemolytic anemia due to oxidative stress. It is not associated with thrombocytopenia or renal failure. The peripheral smear usually shows bite cells. (Choice D) Leukoerythroblastic peripheral smears (ie, nucleated red cells and immature white cells) are usually seen when the marrow is replaced with fibrosis (or metastatic cancer). The red cells can be squeezed while passing through fibrous strands and appear on the peripheral smear as characteristic teardrop cells. Educational objective: Schistocytes suggest microangiopathic hemolytic anemia (eg, hemolytic-uremic syndrome [HUS], thrombotic thrombocytopenic purpura [TTP], disseminated intravascular coagulation [DIC]) or mechanical damage [eg, prosthetic valve]). In childhood, HUS is often preceded by bloody diarrhea. Coagulation studies (prothrombin time and partial thromboplastin time) are normal in HUS-TTP but abnormal in DIC. __________ References: Thrombotic microangiopathies: thrombotic thrombocytopenic purpura/hemolytic uremic syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/21103695)

A 7-Year-Old Boy Comes to the Office for Follow-Up