In medicine, hemolytic-uremic syndrome (or haemolytic-uraemic syndrome, abbreviated HUS) is a disease characterized by hemolytic anemia, acute renal failure (uremia) and a low platelet count (thrombocytopenia).^[1]

It was first defined as a syndrome in 1955.^[2][3]

Signs and symptoms

E. coli O157:H7 increases risk of hemolytic-uremic syndrome.^[4]

Childhood HUS

The classic childhood case of HUS occurs after bloody diarrhea caused by this, a strain of E. coli that expresses verotoxin (also called Shiga-like toxin). The toxin enters the bloodstream, attaches to endothelium (blood vessel lining), causing damage to blood vessels not just in the kidneys but in all tissues of the body, and initiates an inflammatory reaction leading to acute renal failure (ARF) and platelet consumption leading to a low platelet count. However, in contrast with typical Disseminated Intravascular Coagulation (D.I.C.) seen with other causes of septicemia and occasionally with advanced cancer, coagulation factors are not consumed in HUS and the coagulation screen, fibrinogen level, and assays for fibrin degradation products such as "D-Dimers", are generally normal despite the low platelet count. The arterioles and capillaries of the body become obscured by a mesh of activated platelets which have adhered to damaged endothelium. As well as consuming platelets (thrombocytes), this mesh of platelet clot destroys red blood cells as they squeeze through the narrowed blood vessels, via a mechanism known as "microangiopathic hemolysis" which has been likened to the effect of a cheesewire or garotte. This can lead to severe anemia. As in the related condition thrombotic thrombocytopenic purpura (TTP), reduced blood flow through the narrowed blood vessels of the microvascular bed leads to reduced blood flow to vital organs. As the kidneys and the central nervous system (brain and spinal cord) are the parts of the body most critically dependent on a good blood flow, they are the most likely organs to be affected. However, in comparison to TTP, the kidneys tend to be more severely affected in HUS, and the central nervous system much less commonly affected. The usual age of onset is between 2 and adolescence.

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

Adult HUS

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 certain drugs including some chemotherapy drugs and other immunosuppressive agents (mitomycin, ciclosporin, cisplatin and bleomycin).

Familial HUS

A third category is referred to as familial HUS.

It represents 5-10% of HUS cases^{[citation needed]} and is largely due to mutations in the complement proteins factor H, membrane cofactor protein and factor I^[5] leading to uncontrolled complement system activation.

Recurrent thromboses result in a high mortality rate.

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. HUS is characterized by the triad of hemolytic anemia, thrombocytopenia, and acute renal failure. The only distinguishing feature is that in TTP, fever and neurological symptoms are often present; but this is not always the case.

The two conditions are sometimes treated as a single entity called "TTP/HUS".^[6][7] However, some dispute this grouping.^[8]

Treatment

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Antibiotic treatment of O157:H7 colitis may stimulate further verotoxin production and thereby increase the risk of HUS.^{[9] [10]}

Treatment is generally supportive with dialysis as needed. However untreated HUS in adults may progress to end organ damage. Platelet transfusion may actually worsen outcome.

In most children with post-diarrheal HUS, there is a good chances of spontaneous resolution and hence observation in hospital is often all that is necessary, with supportive care such as hemodialysis where indicated. In children with neurological or other non-renal involvement, and in adult cases particularly when there is diagnostic uncertainty between HUS and TTP, plasmapheresis ("plasma exchange") is the treatment of choice. This is generally performed daily until the platelet count is normal, using fresh frozen plasma as the replacement fluid for the patient's plasma which is removed. Plasmapheresis may reverse the ongoing platelet consumption.

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.^[11]

Epidemiology

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

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 1990s, 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

External links

• "About HUS" website

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