Thrombotic Microangiopathies
Profound thrombocytopenia and microangiopathic
hemolytic anemia (red-cell fragmentation) characterize
the thrombotic microangiopathies, which
includes three major disorders: thrombotic thrombocytopenic
purpura, the hemolytic–uremic syndrome,
and the HELLP syndrome (characterized
by pregnancy-related hemolysis, elevated liverenzyme
levels, and low platelet count). The majority
of cases of thrombotic thrombocytopenic purpura
are due to a deficiency of a disintegrin and
metalloproteinase with thrombospondin type 1
motif 13 (ADAMTS13), a disorder that may be
hereditary or caused by autoimmune destruction.
The absence of ADAMTS13 results in the persistence
of high-molecular-weight von Willebrand
factor, which can cause spontaneous platelet aggregation
when the protein is subjected to high
shear stress. The rate of death in untreated cases
is nearly 95%, but with early plasmapheresis, the
survival rate is 80 to 90%. The use of rituximab,
a chimeric monoclonal antibody against the surface
B-cell protein CD20, which leads to destruction
of those cells, has been shown to reduce the
rate of recurrence of the autoimmune form of
this disorder from 57% to 10%.34 Thrombotic
thrombocytopenic purpura is a medical emergency
and in untreated cases is associated with a
rate of death of 90%, usually from myocardial
Thrombotic MicroangiopathiesProfound thrombocytopenia and microangiopathichemolytic anemia (red-cell fragmentation) characterizethe thrombotic microangiopathies, whichincludes three major disorders: thrombotic thrombocytopenicpurpura, the hemolytic–uremic syndrome,and the HELLP syndrome (characterizedby pregnancy-related hemolysis, elevated liverenzymelevels, and low platelet count). The majorityof cases of thrombotic thrombocytopenic purpuraare due to a deficiency of a disintegrin andmetalloproteinase with thrombospondin type 1motif 13 (ADAMTS13), a disorder that may behereditary or caused by autoimmune destruction.The absence of ADAMTS13 results in the persistenceof high-molecular-weight von Willebrandfactor, which can cause spontaneous platelet aggregationwhen the protein is subjected to highshear stress. The rate of death in untreated casesis nearly 95%, but with early plasmapheresis, thesurvival rate is 80 to 90%. The use of rituximab,a chimeric monoclonal antibody against the surfaceB-cell protein CD20, which leads to destructionof those cells, has been shown to reduce therate of recurrence of the autoimmune form ofthis disorder from 57% to 10%.34 Thromboticthrombocytopenic purpura is a medical emergencyand in untreated cases is associated with arate of death of 90%, usually from myocardial
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