Hemolytic Uremic Syndrome (HUS)

Snapshot

• A 4-year-old girl is admitted to the floor with a several day history of bloody diarrhea.  Other members of the daycare she attends also had bloody diarrhea. She is irritable and lethargic. Her skin has also turned slightly yellow. Her arms have multiple petechiae. Lab results show creatinine of 4.0 mg/dL, platelet of 40,000/mm³, and hemoglobin of 7 g/dL. A peripheral blood smear shows schistocytes.

Introduction

• Syndrome commonly seen in children
  • most commonly caused by Escherichia coli O157:H7 (EHEC) 
    • acute diarrhea
    • due to Shiga-like toxin
      • cytokine release, causing HUS
      • does not invade GI mucosa
  • Shigella spp.
    • Shiga toxin
      • cytokine release, causing HUS
      • GI mucosal damage
  • S. pneumoniae infection
• Classic triad
  • thrombocytopenia (first)
  • nonimmune microangiopathic hemolytic anemia (second)
  • acute renal failure (hence, “uremia” in title) (third)
• Similar to TTP but without fever and neurologic symptoms
• Pathogenesis
  • toxin causes cytokine release → damages endothelium
  • microthrombi form at site of damage
    • consumes platelets → thrombocytopenia
    • intravascular mechanical hemolysis → schistocytes
    • decreases renal blood flow → acute renal failure
• Epidemiology
  • most commonly in children
  • exposed to E. coli
    • raw or undercooked meat
    • unwashed fruits/vegetables
• animals at petting zoo

Presentation

• Symptoms
  • prodromal gastrointestinal illness
  • abdominal pain
  • bloody diarrhea
  • nausea
  • vomiting
  • fatigue (anemia)
• Physical exam
  • pallor (anemia)
• jaundice (hemolysis)

Evaluation

• Complete blood count
  • anemia
  • thrombocytopenia
• Peripheral smear
  • schistocytes (helmet cells)
• ↑ serum creatinine
• ↑ bleeding time
• Normal PT/PTT

Differential Diagnosis

• Sepsis
• TTP 
• DIC

Treatment

• Supportive care with fluids to maintain renal perfusion

Prognosis, Prevention, and Complications

• Prognosis
  • 3-5% mortality
  • 5% severe sequelae such as end-stage renal failure
• Prevention
  • prevent EHEC infection
    • avoid raw or undercooked meat
• Complications
  • chronic kidney disease
  • electrolyte abnormalities