Chapter 70

• The thrombotic microangiopathies (TMAs) include the spectrum of thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndromes (HUS) as well as related obstetric syndromes.
• The hallmarks of TMA are a microangiopathic hemolytic anemia (MAHA) and thrombocytopenia.
• TMA must be distinguished from other coagulopathies, such as disseminated intravascular coagulation (DIC) and collagen vascular disease with vasculitis, since therapeutic approaches differ.
• The clinical presentation of TTP/HUS is characterized by a pentad of findings: MAHA, thrombocytopenia, neurologic abnormalities, renal dysfunction, and fever.
• Plasma exchange is the therapy of choice for TTP/HUS, with adjunctive therapies including plasma infusion, corticosteroids, splenectomy, and/or immunosuppressive agents.
• TTP/HUS is a hematologic emergency, and patients are at risk of developing tissue anoxia, lactic acidosis, renal failure, or catastrophic central nervous system injury.
• Plasma exchange may be complicated by catheter accidents, air embolus, citrate toxicity, and pulmonary edema.

Moschcowitz's original description of TTP in 1925 was based on a triad of findings: anemia (of the microangiopathic hemolytic type), thrombocytopenia, and neurologic symptoms. In 1966, 271 cases of TTP were reviewed, and the features of fever and renal impairment were added to form a clinical pentad.1 Subsequent series have confirmed that renal involvement is common, with proteinuria, hematuria, or azotemia seen in 80% of patients with TTP.2,3 Hemolytic uremic syndromes (MAHA, thrombocytopenia, and renal failure) are regarded as part of a spectrum of TMA, which at one end consists of TTP with predominantly neurologic findings and minimal renal abnormality, and at the other end consists of profound renal dysfunction with little or no central nervous system (CNS) pathology. The latter syndromes are more common in childhood, in the postpartum period, and following use of chemotherapeutic (mitomycin C) or immunosuppressive (cyclosporine) agents. On occasion, the evolution of renal manifestations in TTP can become indistinguishable from HUS, so that attempts at rigid distinction are generally unrewarding.4

The age of onset of TTP/HUS ranges from infancy to the eighth decade, with a peak incidence in the third decade. Females are more frequently affected than males by a ratio of 2:1. Childhood HUS often presents with antecedent illness, typically gastroenteritis related to enterotoxin-producing strains of Escherichiacoli or Shigella. TMA associated with pregnancy includes several syndromes with considerable overlap, making prospective differentiation difficult.5,6 Pregnancy-induced hypertension (PIH; eclampsia and pre-eclampsia) is often associated with subtle laboratory abnormalities consistent with a degree of underlying TMA; on occasion this becomes clinically significant. When hypertension, elevated liver enzyme levels, and a low platelet count occur together as a syndrome in the peripartum period, the term HELLP syndrome is applied (see Chap. 105). TTP may also be encountered in the second or third trimesters of pregnancy; unlike thrombocytopenias associated with PIH, it may not improve rapidly with termination of the pregnancy and may require further treatment. Finally, postpartum HUS is distinguished by its onset after delivery. Characterization of TMA in pregnancy is often made in ...

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