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Hemolytic Uremic Syndrome–Associated Encephalopathy

• Background:
  • Hemolytic uremic syndrome (HUS) belongs to a range of thrombotic microangiopathies and stems from endothelial cell injury.
  • HUS encompasses several disorders including Shiga toxin–induced and pneumococcus-induced HUS, and HUS secondary to other causes such as infections, drugs, cancer, and systemic diseases, with 90% of cases occurring after a gastrointestinal infection with Shiga toxin–producing bacteria.
• Clinical Presentation:
  • Severe abdominal pain and diarrhea, often bloody, begin several days after food contaminated with Shiga toxin E Coli (STEC) is consumed.
  • The classic triad combines thrombocytopenia, hemolytic mechanical anemia, and acute kidney injury.
  • As gastrointestinal concerns resolve, other symptoms may arise from ischemic or direct toxin-related damage to various organs, notably the kidneys and the brain.
  • Central nervous system involvement may occur in as many as 20–50% of cases, and, in these cases, patients may experience seizures, aphasia, delirium, pyramidal and extrapyramidal symptoms, and coma.
• Key Diagnostic Features:
  • MR imaging often demonstrates nonexpansile, typically symmetric T2/FLAIR hyperintensities involving the lateral thalamus, the paramedian dorsal pons, and with variable involvement of the basal ganglia and lentiform nuclei, mesiotemporal lobes, centrum semiovale white matter, and cerebellum, likely due to a toxin-induced neuronal edema.
  • Associated hemorrhage, diffusion restriction, and enhancement are not typically present.
  • Shiga toxin is identified by means of stool analyses during the acute colitis phase but may not be identifiable when STEC-HUS begins.
  • Blood test findings suggestive of hemolytic uremic syndrome include schistocytes on peripheral blood smear, thrombocytopenia, and acute kidney injury.
• Differential Diagnosis:
  • Wernicke encephalopathy: T2/FLAIR hyperintensities +/- enhancement within the mammillary bodies, hypothalamus, medial thalamus, and periaqueductal gray matter
  • Viral encephalitis: Location of potential signal abnormalities dependent on underlying cause
  • Creutzfeldt-Jakob disease: Symmetric FLAIR/DWI hyperintense signal involving pulvinar and dorsomedial thalamus (variant) and along cerebral cortex (sporadic)
  • Osmotic demyelination: central pontine T2 hyperintensity or extrapontine involvement (cerebellum, basal ganglia)
• Treatment:
  • Management of STEC-HUS revolves around supportive care including fluids and electrolytes, antihypertensive agents, anticonvulsant agents for seizures, and nutritional support. Eculizumab may be helpful in some refractory cases.
  • Antibiotic therapy is not recommended, as Shiga toxin–producing bacteria (typically E. coli O157:H7 strain) are known to be resistant to most antibiotic treatments.
  • Early and aggressive hydration efforts with IV fluid infusion may reduce rates of CNS involvement and other complications. Neurologic outcome is typically favorable with appropriate therapy, and brain signal abnormalities typically resolve.
November 3, 2022

A 56-year-old woman presents to the emergency department with aphasia and acute encephalopathy. Initial noncontrast head CT/CTP/CTA are all negative for acute infarction, hemorrhage, and major vessel occlusion. The patient then reports abdominal pain, experiencing both diarrhea and coffee ground emesis. Laboratory results yield findings consistent with renal failure and thrombocytopenia; stool analysis yields Shiga toxin.

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