| Discussion: Fairly unusual presentation for HUS as many times the GI illness has resolved when renal failure begins.
HUS is characterized by acute renal failure, microangiopathic hemolytic anemia, fever, and thrombocytopenia. Diarrhea and upper respiratory infection are the most common precipitating factors. HUS is one of the most common causes of acute renal failure in children. The term HUS was first used by Gasser and coworkers in 1955, when they described an acute fatal syndrome in children that featured hemolytic anemia, thrombocytopenia, and severe renal failure.
In children, HUS often follows a prodromal infectious disease, usually diarrhea (90%) and less often an upper respiratory infection (10%). Use of antimotility drugs may increase the risk of developing HUS. The most common cause of HUS is a toxin produced by Escherichia coli serotype 0157:H7. Additional agents include Shigella, Salmonella, Yersinia, and Campylobacter species. The shiga and shigalike toxins, produced by some strains of Shigella dysenteriae and E coli 0157:H7, respectively, have been associated with approximately 70% of cases of HUS in children. Because of the cytotoxic activity of these toxins on vero cells, they are referred to as verotoxins. Transmission of E coli 0.57:H7 appears to be caused by contaminated food, such as ground beef and other cattle products that are undercooked, and unpasteurized dairy products. Food contaminated with E coli does not look, smell, or taste bad.
Person-to-person contact, as well as contamination of public water supplies, may also have a role in the transmission of this bacterium. E coli is normal flora in the gastrointestinal tracts of some healthy cattle, and children can contract it by petting a cow.
HUS is also associated with viruses, including varicella, echovirus, and coxsackie A and B, as well as other infectious agents such as Streptococcus pneumoniae and Clostridium difficile. HUS has also been associated with AIDS, cancer, and the administration of chemotherapeutic agents. Mitomycin C is the most common chemotherapeutic agent associated with HUS. Malignancies found in conjunction with HUS include prostatic, gastric, and pancreatic malignancies. Some have suggested that HUS is mediated by immune complexes. Some cases of HUS are familial, which may reflect a genetic or human leukocyte antigen (HLA)–type predisposition.
HUS and thrombotic thrombocytopenic purpura (TTP) represent different ends of what is probably the same disease continuum. Endothelial cell injury appears to be the primary event in the pathogenesis of these disorders. The endothelial damage triggers a cascade of events that result in microvascular lesions with platelet-fibrin hyaline microthrombi that occlude arterioles and capillaries. The platelet aggregation results in a consumptive thrombocytopenia. The epithelial damage may result from toxins released by bacteria or viruses. In TTP, the hyaline microthrombi occur throughout the microcirculation, and microvascular thromboses may be found in the brain, skin, intestines, skeletal muscle, pancreas, spleen, adrenals, and heart. On the other hand, in HUS, microthrombi are essentially confined to the kidneys. Many of the infectious agents and drugs implicated in HUS/TTP are toxic to the vascular endothelium.
Although the vascular lesions are identical in HUS and TTP, involvement of the CNS predominates in TTP. Renal involvement is the defining feature of HUS. On gross examination, the kidneys are swollen and pale; many fleabite hemorrhages are on the surface. In HUS and TTP, the platelet and fibrin microthrombi within the renal microvasculature are accompanied by thrombocytopenia and a microangiopathic hemolytic anemia. Vasculitis is usually absent.
Recurrences of HUS have been reported, and they are noted to have a mortality rate of 30%.
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12 Y/O BOY WITH 2-3 DAYS DIARRHEA.
