The term thrombotic thrombocytopenic purpura-hemolytic uremic syndrome (TTP-HUS) describes acute syndromes with abnormalities in multiple organ systems (table 1). Although these syndromes have multiple different etiologies, different demographics, different responses to treatment, and different prognoses, their presenting features are similar in many patients: thrombocytopenia and microangiopathic hemolytic anemia without another apparent cause and, in many patients, neurologic and/or renal abnormalities [1,2].
- In some patients, neurologic abnormalities are dominant and acute renal failure is minimal or not present; these patients are considered by some to represent classical or "idiopathic" TTP, typically associated with severe ADAMTS13 deficiency.
- In other patients, acute renal failure is dominant and neurologic abnormalities are minimal or absent; these patients are considered by some to represent HUS. However, some patients present with both severe neurologic abnormalities, such as seizures and coma, and acute renal failure, making this distinction difficult.
- Some patients may have thrombocytopenia and microangiopathic hemolytic anemia with no neurologic or renal abnormalities. For example, over half of patients with severe ADAMTS13 deficiency have no or minimal neurologic or renal abnormalities (table 2).
Therefore, when these patients are initially evaluated, they can best be described by the comprehensive term TTP-HUS. An additional justification for the use of the term TTP-HUS is that the pathologic changes in patients described as having TTP or HUS are identical and the initial treatment of all adult patients is the same: plasma exchange [1,2]. (See 'Evolution of disease definitions' below.)
As a result, these syndromes in adults will be considered together and referred to as TTP-HUS; the one exception is “typical” childhood HUS following an episode of abdominal pain and diarrhea that is often bloody, due most often to Shiga toxin-producing enterohemorrhagic Escherichia coli (table 1) [1,2]. This syndrome of children has the important difference that plasma exchange treatment is not a standard initial treatment.
The causes of TTP-HUS will be discussed here. The clinical manifestations, diagnosis, and treatment of TTP-HUS are discussed separately. (See "Diagnosis of thrombotic thrombocytopenic purpura-hemolytic uremic syndrome in adults" and "Treatment and prognosis of thrombotic thrombocytopenic purpura-hemolytic uremic syndromes in adults".)