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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]
E. coli O157:H7 increases risk of hemolytic-uremic syndrome.[4]
The classic childhood case of HUS occurs after bloody diarrhea caused by 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 (DIC) 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 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).
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