Thrombotic Thrombocytopenic Purpura and Hemolytic-Uremic Syndrome
Thrombotic thrombocytopenic purpura (TTP) and hemolytic-uremic syndrome (HUS) are severe, serious disorders that involve the formation of small blood clots throughout the body that block the flow of blood to vital organs such as the brain, heart, and kidneys.
TTP and HUS are rare, related disorders in which many small blood clots (thrombi) form suddenly throughout the body. These blood clots block small blood vessels throughout the body, particularly those in the brain, heart, and kidneys. The blood vessel blockage damages organs and can break apart red blood cells that pass through partially blocked vessels. The blood clots also mean that an abnormally high number of platelets are being used, which leads to a sharp decrease in the number of platelets in the bloodstream. Platelets are cell fragments that circulate in the bloodstream and help blood clot (see also Overview of Platelet Disorders). Platelets are sometimes called thrombocytes, and having too few platelets is termed thrombocytopenia.
The main differences between TTP and HUS are that TTP is more common in adults and does not often cause kidney failure (acute kidney injury), whereas HUS is more common in children and typically causes kidney failure.
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The cause of TTP is often unknown, but some people develop it after taking certain drugs (including quinine, cyclosporine, and mitomycin C) or during pregnancy. In other people, TTP can be an autoimmune disorder in which the body's immune system creates antibodies that destroy an enzyme (ADAMTS13). When this enzyme is deficient, platelets start to clot inappropriately within blood vessels, the number of platelets in the blood (platelet count) decreases, and the organs in which the clots occur (such as the brain and kidneys) can be damaged.
HUS usually occurs following an intestinal infection that results from ingestion of food contaminated with Escherichia coliO157:H7 or other toxin-producing bacteria.
In TTP and HUS, symptoms develop suddenly.
Symptoms in TTP and HUS are quite distinct from symptoms of most other forms of thrombocytopenia.
In TTP, the small blood clots that develop (using up platelets) cause a wide range of symptoms and complications, some of which can be life threatening. Symptoms that result from clots in the brain may include headache, confusion, seizures, and coma. Symptoms that result from clots in the brain may come and go and may vary in severity. Symptoms that result from clots elsewhere in the body include abnormal heart rhythms, blood in the urine , and abdominal pain.
In HUS, children usually first have vomiting and diarrhea. The diarrhea is often bloody. The main symptoms of complications of HUS are related to blood clots that develop in the kidneys, causing damage that is usually severe and often progresses to kidney failure requiring dialysis. HUS does not often cause brain symptoms.
Doctors suspect TTP or HUS when they find a low platelet count in people who have been ill, who have taken certain drugs, or who are pregnant. Although there are no blood tests that specifically diagnose TTP and HUS, doctors do a number of blood test that together with people's symptoms help make the diagnosis. These blood tests often include tests demonstrating that red blood cells are being destroyed and tests to detect the presence of antibodies against the ADAMTS13 enzyme.
HUS is diagnosed when acute kidney injury is identified by blood tests that show high levels of urea and creatinine.
With TTP, people are often treated with corticosteroids and plasma exchange (plasma transfusions along with plasmapheresis—see Plateletpheresis).
With HUS, about half of children temporarily require kidney dialysis. Most often, the kidneys recover, but some children have permanent kidney damage. Plasma exchange is not useful. Eculizumab is an antibody that reduces the rate of kidney damage, and in some people, it may rapidly restore kidney function.