Hemolytic-uremic syndrome

In medicine, hemolytic-uremic syndrome (or haemolytic-uraemic syndrome, abbreviated HUS) is a disease characterized by microangiopathic hemolytic anemia, acute renal failure and a low platelet count (thrombocytopenia).

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Signs and symptoms

The classic childhood case of HUS occurs after bloody diarrhea caused by E. coli O157:H7, a strain of E. coli that expresses verotoxin (also called Shiga toxin). The toxin enters the bloodstream, attaches to renal endothelium and initiates an inflammatory reaction leading to acute renal failure (ARF) and disseminated intravascular coagulation (DIC). The fibrin mesh destroys red blood cells and captures thrombocytes, leading to a decrease of both on complete blood count. The usual age of onset is between 2 and adolescence.

HUS occurs after 2-7% of all E. coli O157:H7 infections.

Adult HUS has similar symptoms and pathology but is an uncommon outcome of the following: HIV; antiphospholipid syndrome (associated with Lupus erythematosus and generalized hypercoagulability); post partum renal failure; malignant hypertension; scleroderma; and cancer chemotherapy (mitomycin, cyclosporine, cisplatin and bleomycin).

A third category is referred to as Familial HUS. It represents 5-10% of HUS cases and is largely due to mutations in the complement proteins factor H, membrane cofactor protein and factor I leading to uncontrolled complement system activation. Recurrent thromboses result in a high mortality rate.

Epidemiology

HUS has a peak incidence between 6 months and 4 years of age.^[1]

Diagnosis

Clinically, HUS can be very hard to distinguish from thrombotic thrombocytopenic purpura (TTP). The laboratory features are almost identical, and not every case of HUS is preceded by diarrhea. The only distinguishing feature is that in TTP, neurological symptoms occur more often, but this is not always the case.

Treatment

Treatment is generally supportive with dialysis as needed. Platelet transfusion may actually worsen outcome.

In severe cases or when there is diagnostic uncertainty between HUS and TTP, plasmapheresis is the treatment of choice.

Prognosis

With aggressive treatment > 90% survive acute phase. About 9% may develop end stage renal disease. About one-third of persons with hemolytic-uremic syndrome have abnormal kidney function many years later, and a few require long-term dialysis. Another 8% of persons with hemolytic uremic syndrome have other lifelong complications, such as high blood pressure, seizures, blindness, paralysis, and the effects of having part of their colon removed. The overall mortality rate from HUS is 5-15%. Older children and adults have a worse prognosis.^[2]

Impact on society

HUS and the E. coli infections which caused it have been the source of much negative publicity for the Food and Drug Administration (FDA), meat industries, and fast-food restaurants since the 1990's, especially in the Jack in the Box contaminations. It was also featured in the Robin Cook novel Toxin. In 2006, an epidemic of harmful E. coli emerged in the United States due to contaminated spinach. 183 known cases have been reported, including 29 cases of HUS.

See also

• E. coli O157:H7
• Shigellosis
• Microangiopathic hemolytic anemia

References

1. ^ Corrigan JJ Jr, Boineau FG (2001). "Hemolytic-uremic syndrome". Pediatr Rev 22 (11): 365-9. PMID 11691946.
2. ^ Chu P, Hemphill RR (2004). "222: Acuired hemolytic anemia", in Tintinalli JE, Kelen GD, Stapczynski JS: Emergency Medicine: A Comprehensive Study Guide, 6th Edition, New York, NY: McGraw-Hill.  ISBN 0-07-138875-3