Renal · Glomerular Diseases
The facts most likely to be tested
The classic triad of Hemolytic Uremic Syndrome (HUS) consists of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury.
Typical HUS is most commonly caused by Shiga toxin-producing E. coli (STEC), often following a prodrome of bloody diarrhea.
Peripheral blood smear in HUS reveals schistocytes (fragmented red blood cells) due to mechanical shearing in damaged microvasculature.
Antibiotics are contraindicated in STEC-associated HUS because they increase the release of Shiga toxin and elevate the risk of progression to renal failure.
The pathophysiology involves endothelial cell injury leading to platelet microthrombi formation in the renal microcirculation.
Management of typical HUS is primarily supportive care, including aggressive fluid resuscitation and dialysis if indicated for severe renal failure.
Atypical HUS is characterized by dysregulation of the alternative complement pathway and is often treated with eculizumab.
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A 4-year-old boy is brought to the emergency department with a 3-day history of bloody diarrhea and abdominal pain. Physical examination reveals pallor and petechiae on the lower extremities. Laboratory studies show a hemoglobin of 7.2 g/dL, a platelet count of 65,000/µL, and a serum creatinine of 2.1 mg/dL. A peripheral blood smear demonstrates numerous schistocytes.
What is the most appropriate management for this patient?
Supportive care with fluid resuscitation
The patient presents with the classic triad of HUS following a diarrheal illness; because this is STEC-associated HUS, antibiotics are contraindicated, and management is strictly supportive.
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Etiology / Epidemiology
Primarily affects children following Shiga toxin-producing E. coli (STEC) infection, typically serotype O157:H7.
Clinical Manifestations
Classic triad: microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury.
Diagnosis
Diagnosis is clinical; peripheral blood smear shows schistocytes; stool culture or PCR for Shiga toxin.
Treatment
Management is supportive care; avoid antibiotics and avoid anti-motility agents.
Prognosis
Most recover with supportive care; chronic kidney disease occurs in ~25% of severe cases.
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Epidemiology & Etiology
Most common cause of acute renal failure in children. Often follows ingestion of undercooked ground beef or contaminated produce. The prodrome typically involves bloody diarrhea 5-10 days prior to systemic onset.
Pertinent Anatomy
The primary site of injury is the renal microvasculature. Endothelial damage leads to localized thrombosis within the glomerular capillaries.
Pathophysiology
Shiga toxin enters the bloodstream, causing endothelial cell injury and activation of the coagulation cascade. This results in microangiopathic hemolytic anemia (MAHA) as RBCs are sheared by fibrin strands. Platelet consumption leads to thrombocytopenia, while glomerular microthrombi cause acute kidney injury.
Clinical Manifestations
Patients present with the classic triad of pallor (anemia), petechiae/purpura (thrombocytopenia), and oliguria/anuria (renal failure). Neurologic changes such as seizures or altered mental status indicate severe disease. Bloody diarrhea is the hallmark prodrome.
Diagnosis
The peripheral blood smear is the gold standard for identifying schistocytes (helmet cells). Labs reveal elevated LDH, low haptoglobin, and elevated creatinine. Stool culture or PCR confirms the presence of Shiga toxin.
Treatment
Treatment is strictly supportive care, including fluid resuscitation and dialysis if indicated. Antibiotics are contraindicated as they increase the risk of toxin release. Anti-motility agents are strictly avoided as they increase toxin exposure time.
Prognosis
Prognosis is generally favorable with supportive care; mortality is <5%. Long-term monitoring for hypertension and proteinuria is required to detect chronic kidney disease.
Differential Diagnosis
TTP: characterized by fever and severe neurologic symptoms; ADAMTS13 deficiency
DIC: associated with abnormal coagulation studies (PT/PTT) and underlying sepsis
ITP: isolated thrombocytopenia without anemia or renal involvement
HUS (atypical): complement-mediated; lacks bloody diarrhea prodrome
SLE: systemic symptoms with positive ANA and anti-dsDNA