Hemolytic uremic syndrome
Hemolytic uremic syndrome, HUS, is a condition characterized by the destruction of red blood cells and kidney failure that is associated with microangiopathic hemolytic anemia and thrombocytopenia. HUS is a serious illness and potentially fatal.
There is clumping of platelets (the blood cells responsible for clotting) within the kidney's small blood vessels with resultant ischemia (reduced blood flow) leading to the kidney failure. The partial blockage of the blood vessels also leads to the destruction of red blood cells (hemolysis). Platelets are also decreased which can cause bleeding problems.
Hemolytic" refers to the breakup of red blood cells. This leads to anemia and a shortage of platelets (thrombocytopenia) which causes abnormal bleeding. "Uremic" refers to the acute kidney failure. Central nervous system problems with seizures and coma can also occur.
Hemolytic-uremic syndrome (HUS) is the most common cause of acute renal failure in children and is increasingly recognized in adults. Thrombotic thrombocytopenic purpura (TTP), childhood HUS, and adult HUS differ in their clinical presentations, but these conditions have many common features. Cases of HUS typically begin with severe abdominal cramps and diarrhea which may become bloody by the second or third day. Nausea and vomiting is present in approximately half of the patients. Most patients recover in 7-10 days, but some (6%) go on to have HUS. This is most likely to happen in children and the elderly. Some patients develop neurological problems such as seizures. Many patients require dialysis and blood transfusions. The mortality rate is 3 to 5%.
Hemolytic-uremic syndrome (HUS) is classified into 2 main categories, depending on whether it is associated with Shiga-like toxin.
Shiga-like toxin (Stx)–associated HUS (Stx-HUS) is the classic or typical, primary or epidemic form of hemolytic-uremic syndrome (HUS). Stx-HUS is largely a disease of children younger than 2-3 years and often results in diarrhea (denoted D+HUS). One fourth of patients present without diarrhea (denoted D-HUS). Acute renal failure occurs in 55-70% of patients, but they have a favorable prognosis, and as many as 70-85% of patients recover renal function.
Non–Stx-associated HUS (non–Stx-HUS) can be sporadic or familial. As the name implies, infection by Stx-producing bacteria is not the cause, and disease may occur year-round without a gastrointestinal prodrome (D-HUS). Overall, patients with non–Stx-HUS have a poor outcome, and as many as 50% may progress to end-stage renal disease (ESRD) or irreversible brain damage. Up to 25% of patients die during the acute phase. The familial form is associated with genetic abnormalities of the complement regulatory proteins.
Most cases of HUS occur after an infection in the digestive system that has been caused by toxin-producing strains of the bacterium Escherichia coli. About 75% of HUS cases in children are caused by the strain referred to as E. coli O157:H7, which is found in the intestinal tract of cattle, while the remaining cases are caused by non-O157 strains. Some children infected with E. coli O157:H7 will develop HUS. HUS also can follow respiratory infection episodes in young children. HUS has also been known to occur in persons using drugs such as oral contraceptives, immunosuppressors, and antineoplastics, and in women during the postpartum period.