Acquired Thrombotic Thrombocytopenic Purpura

Conventionally, thrombotic thrombocytopenic purpura (TTP) has been defined as a syndrome of thrombocytopenia and microangiopathic hemolysis (MAHA) without another plausible cause. In some versions of the definition, neurologic deficits (triad), renal abnormalities, and fever (pentad) are also included in the diagnostic criteria. These definitions of TTP fail to distinguish among the various causes of thrombocytopenia and MAHA. The discovery of ADAMTS13 and its deficiency in a subset of conventionally defined “TTP” has broadened our knowledge and transformed our views on how to define TTP as a disease. With a mechanistic definition, it is now possible to distinguish TTP from other causes of MAHA, to make the diagnosis of TTP in patients without thrombocytopenia or MAHA, and to manage the disease more rationally.