Thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening thrombotic microangiopathy marked by severe ADAMTS13 deficiency, platelet-rich microclots, thrombocytopenia, and red-cell fragmentation.

ADAMTS13: A plasma metalloprotease that cleaves unusually large von Willebrand factor multimers into smaller forms. Its severe deficiency is the defining biochemical defect in TTP.
Plasma exchange: A treatment that removes a patient's plasma and replaces it with donor plasma or another fluid. It removes anti-ADAMTS13 antibodies and supplies functional ADAMTS13 in immune TTP.
Immune-mediated thrombotic thrombocytopenic purpura: TTP caused by autoantibodies that inhibit ADAMTS13 or accelerate its clearance. This acquired form accounts for most TTP cases.
Hemolytic uremic syndrome: A thrombotic microangiopathy in which kidney injury is prominent, often associated with Shiga toxin or complement dysregulation. It can resemble TTP, but severe ADAMTS13 deficiency points instead to TTP.
Pentad of thrombotic thrombocytopenic purpura: The historical combination of thrombocytopenia, hemolytic anemia, neurologic abnormalities, fever, and kidney dysfunction in TTP. The full pentad is uncommon; treatment should not wait for all five findings.
Von Willebrand factor: A blood-plasma glycoprotein that supports platelet adhesion and carries coagulation factor VIII. Uncleaved, unusually large multimers bind platelets and promote microvascular clots.
Caplacizumab: An antibody fragment that blocks the interaction between von Willebrand factor and platelets. It rapidly limits platelet-rich microthrombus formation while TTP treatment takes effect.
Congenital thrombotic thrombocytopenic purpura: An inherited TTP form caused by pathogenic variants in both copies of the ADAMTS13 gene. It causes persistent enzyme deficiency without an acquired ADAMTS13 autoantibody.
Shiga toxin-producing Escherichia coli: A group of E. coli strains that produce toxins capable of causing bloody diarrhea and hemolytic uremic syndrome. Its toxin can cause a diarrheal microangiopathy that must be distinguished from TTP.
Neurologic manifestations of thrombotic thrombocytopenic purpura: Neurologic symptoms in TTP, ranging from confusion and headache to seizures or focal deficits. Fluctuating neurologic signs reflect microvascular injury and can prompt urgent evaluation.

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