Thrombotic Thrombocytopenic Purpura (TTP)
Thrombotic means that blood clots form, thrombocytopenic means the platelet count is low, and purpura means that purple spots or bruises appear on the skin. Thrombotic thrombocytopenic purpura (TTP) is a rare disorder in which many small blood clots (thrombi) form suddenly throughout the body. It is related to hemolytic-uremic syndrome (HUS), but it is more likely to occur in adults than HUS. The 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 up, which leads to a sharp decrease in the number of platelets in the bloodstream.
Platelets are cells that are made in the bone marrow and circulate in the bloodstream and help blood clot. Platelets are sometimes called thrombocytes. Having too few platelets is termed thrombocytopenia.
The cause of TTP is often unknown, but some people develop it after taking certain drugs (including quinine, cyclosporine, and mitomycin C), after certain types of intestinal infection, during pregnancy, or rarely as an inherited disease. In most people, TTP is 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.
In thrombotic thrombocytopenic purpura (TTP), symptoms develop suddenly.
Symptoms in TTP 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.
Doctors suspect thrombotic thrombocytopenic purpura (TTP) 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, doctors do a number of blood tests that, together with people's symptoms, help make the diagnosis. These blood tests often include tests demonstrating that red blood cells are being destroyed, tests to see how well the kidneys are working, and often tests to detect the presence of antibodies against the ADAMTS13 enzyme.
With thrombotic thrombocytopenic purpura (TTP), people are often treated with corticosteroids and plasma exchange (plasma transfusions along with plasmapheresis). In plasmapheresis, blood is taken from the person and put in a machine that separates the blood cells from the liquid part of the blood (plasma). The plasma, which contains disease-causing antibodies, is discarded and the blood cells are returned to the person.
Rituximab is a drug that suppresses the immune system and is sometimes used in people with TTP who relapse after being treated with corticosteroids and plasmapheresis.
Caplacizumab is a new drug that inhibits the interaction between a protein involved in clotting and platelets. Although caplacizumab may reduce the need for plasma exchange and speed recovery in TTP, it may increase the risk of bleeding.