[Thrombotic thrombocytopenic purpura - a rare diagnosis].

Thrombotic thrombocytopenic purpura (TTP) is a rare life-threatening thrombotic microangiopathy (TMA) characterized by a microangiopathic hemolytic anemia and severe thrombocytopenia, due to platelet consumption. Microthrombi form in small vessels, leading to organ ischemia, most commonly in the central nervous system (CNS). The pathophysiology of TTP is related to a deficiency of ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), an enzyme that cleaves the von Willebrand multimer. In the absence of ADAMTS13, the von Willebrand multimer is unfolded into an elongated active form that causes platelet activation and aggregation in arterioles and capillaries. Acquired TTP is caused by autoantibodies against ADAMTS13.  The hemolytic anemia is typically DAT-negative and caused by shattering of erythrocytes when passing the microthrombi. Rapid recognition is crucial for the outcome and to initiate the appropriate treatment. It may take several days to get the test results for ADAMTS13 and when there is a high clinical probability for TTP, plasmapheresis must be initiated pending test results. PLASMIC score can be used in determining the probability of low ADAMTS13 in a hospitalized patient with thrombocytopenia and hemolysis to identify the patients that could benefit from early TTP-specific treatment.  First line treatment for acute TTP includes daily plasma exchange, steroids and rituximab. Caplacizumab is an anti-von-Willebrand factor-directed antibody fragment that targets the A1 domain of the von Willebrand factor, thereby inhibiting the interaction between von Willebrand factor multimers and platelets. The treatment has been shown to have beneficial effects when added to standard treatment, without having immunosuppressive effects.