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Terminology and outcomes definitions for thrombotic thrombocytopenic purpura (TTP)

Terminology and outcomes definitions for thrombotic thrombocytopenic purpura (TTP)
Syndromes
Thrombotic microangiopathy (TMA) Condition in which small vessel microthrombi form and cause thrombocytopenia (platelet count <150,000/microL) and microangiopathic hemolytic anemia (MAHA; schistocytes and evidence of hemolysis)
Thrombotic thrombocytopenic purpura (TTP) TMA caused by severe deficiency of the ADAMTS13 protease, which cleaves large VWF multimers
  • Immune TTP
 Acquired TTP caused by an autoantibody against ADAMTS13
  • Hereditary TTP
 Genetic condition caused by biallelic variants in the ADAMTS13 gene
Outcomes of therapy for immune TTP
Clinical response

Resolution of thrombocytopenia and hemolysis

-and-

Cessation of clinical deterioration
Remission Sustained response after stopping TPE and/or anti-VWF therapy
  • Clinical remission

Sustained clinical response for ≥30 days

-or-

ADAMTS13 remission (partial or complete)
  • ADAMTS13 remission (partial)
 ADAMTS13 activity ≥20% but below the assay's lower limit of normal
  • ADAMTS13 remission (complete)
 ADAMTS13 activity above the assay's lower limit of normal
Relapse Clinical and/or laboratory deterioration following remission
  • Clinical relapse
 Recurrence of thrombocytopenia following a remission, without another cause (subsequently must be confirmed by documenting ADAMTS13 activity <10%)
  • ADAMTS13 relapse
 ADAMTS13 activity <20% following an ADAMTS13 remission
Exacerbation Recurrence of thrombocytopenia without another cause following a response but ≤30 days after stopping TPE or anti-VWF therapy
Refractory disease Lack of a clinical response to initial treatment*
Refer to separate discussions in UpToDate for the approach to managing immune TTP, hereditary TTP, and other TMAs.
  • Clinical remission can occur without ADAMTS13 remission, but ADAMTS13 remission is always accompanied by clinical remission.
  • Clinical relapse is always accompanied by ADAMTS13 relapse, but ADAMTS13 relapse can occur without clinical relapse.
  • Preemptive treatment of ADAMTS13 relapse can induce ADAMTS13 remission and reduce the risk of clinical relapse.
Anti-VWF therapy includes caplacizumab and other therapies under development.
VWF: von Willebrand factor; TPE: therapeutic plasma exchange; LLN: lower limit of normal; DIC: disseminated intravascular coagulation.
* Refractory disease is rare in the era of rituximab and anti-VWF therapy. If thrombocytopenia persists despite TPE, rituximab, and anti-VWF therapy, other potential causes such as sepsis, DIC, and drug-induced thrombocytopenia should be investigated.
Adapted from: Cuker A, Cataland SR, Coppo P, et al. Redefining outcomes in immune TTP: An international working group consensus report. Blood 2021; 137:1855.
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