title: Thrombotic microangiopathies.
abstract: OBJECTIVE
  To review the clinical features and pathophysiologic mechanisms of the thrombotic microangiopathies (TMAs) including acquired and congenital thrombotic thrombocytopenic purpura (TTP), Shiga toxin-induced and atypical (non-Shiga toxin-induced) hemolytic uremic syndrome (HUS), and the TMAs associated with pregnancy, drugs, and organ transplantation.
  
  
  METHODS
  PubMed Medline was used to identify articles published from 2000 to July 2013 using the following key words: thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, Shiga toxin, ADAMTS13, and eculizumab. Articles in languages other than English, papers available in abstract form only, and nearly all single case reports were excluded. Small series, reports from registries and study groups, reviews, guidelines, and articles concerning pathophysiology and therapy were preferentially considered.
  
  
  RESULTS
  Impaired post-secretion processing of unusually large von Willebrand multimers due to deficiency of ADAMTS13 (IgG antibodies or congenital), dysregulation of the alternative complement pathway (mutations and/or specific antibodies), and endothelial injury are pathophysiologic mechanisms involved in the TMAs. Acquired and congenital TTP are due primarily to severe ADAMTS13 deficiency, atypical HUS is commonly associated with complement dysregulation, and Shiga toxin, drugs, immune complexes, and others likely damage endothelium. However, there is considerable mechanistic overlap, and the TMAs often have multifactorial causation. Plasma procedures, complement pathway inhibition, immunosuppression, and general supportive care are the principal therapies.
  
  
  CONCLUSIONS
  The TMAs are very important conditions because of their associated organ damage and mortality rates. Prompt recognition and categorization by both clinical presentation and pathophysiologic mechanisms should become routine as they are crucial to an optimal treatment plan. Treatment advances have substantially reduced the morbidity of these disorders. Investigational therapies are promising.
authors.affiliation: UCLA Division of Hematology-Oncology, David Geffen School of Medicine at the University of California, 100 UCLA Medical Plaza, Suite 550, Los Angeles, CA 90095. Electronic address: mrosove@mednet.ucla.edu.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Rosove
mesh_terms: D051722:ADAM Proteins / Q000276:immunology; D000071120:ADAMTS13 Protein; D061067:Antibodies, Monoclonal, Humanized / Q000627:therapeutic use; D065766:Atypical Hemolytic Uremic Syndrome / Q000378:metabolism / Q000628:therapy; D006463:Hemolytic-Uremic Syndrome / Q000276:immunology / Q000378:metabolism* / Q000628:therapy; D006801:Humans; D011697:Purpura, Thrombotic Thrombocytopenic / Q000276:immunology / Q000378:metabolism* / Q000628:therapy; D022621:Shiga Toxin / Q000276:immunology; D057049:Thrombotic Microangiopathies / Q000276:immunology / Q000378:metabolism / Q000628:therapy
chemical_list: D061067:Antibodies, Monoclonal, Humanized; D022621:Shiga Toxin; C481642:eculizumab; D051722:ADAM Proteins; D000071120:ADAMTS13 Protein; C099604:ADAMTS13 protein, human
keywords: Complement dysregulation; Eculizumab; Hemolytic uremic syndrome; Shiga toxin; Thrombotic microangiopathy; Thrombotic thrombocytopenic purpura