Adult autoimmune throbocytopenic
purpura (
ATP) is a platelet disorder that develops in certain individuals with a genetic as well as sex (female) predisposition following an environment event (?viral). This results in the production of an
IgG antiplatelet antibody capable of reacting with the host's platelets, as well as crossing the placenta. This leads to the rapid clearance and destruction of opsonized platelets by the reticuloendothelial system, particularly the spleen, by greater than tenfold the normal rate. Bound platelet
IgG correlates with disease severity, whereas serum antiplatelet
IgG does not. It has not been rigorously established whether bound platelet
IgG is directed against a platelet
antigen or represents an
immune complex bound to the platelet
Fc receptor. Nevertheless, several lines of evidence suggest that antiplatelet
IgG binds directly to a platelet
antigen(s). Megakaryocyte number, volume, and mass are increased commensurate with increased platelet turnover. Platelets of increased size, megathrombocytes, are noted on peripheral smear or via platelet volume distribution analysis. Megathrombocyte number is proporationate to megakarocyte number and to platelet turnover. Megathrombocyte diameter is inversely proportional to platelet survival. Antiplatelet antibody is also associated with qualitative platelet functional defects, which are indistinguishable from those noted with thrombopathia (i.e., apparent platelet release defect). Antibody-induced functional defects are probably more common than quantitative thrombocytopenic defects and may represent a significant portion of those women with the "easy bruising" syndrome and normal platelet count. Adults who develop
ATP generally develop the chronic variety, which remains permanently with the patient. Treatment should be directed towards maintaining the patient free of
purpura, not restoring the platelet count to normal. This can generally be accomplished with a platelet count of > 40,000/cu mm with patients having this disorder. Approximately 50% of patients respond to
steroids by a significant elevation of platelet count and improvement of
purpura. However, cessation of
therapy results in eventual relapse if the disease is of the chronic variety.
Splenectomy is successful in approximately 65-75% of patients, resulting in a restoration of the platelet count to normal or safe levels by removing a major source of platelet destruction as well as antibody production; platelet survival improves. At least 50% of patients "in remission" following
steroids or
splenectomy generally have a compensated thrombocytolytic state in which increased platelet production keeps up with increased platelet destruction. Antiplatelet
IgG can often be found in the serum of these patients. Patients refractory to
steroids and/or
splenectomy present with a serious therapeutic problem. Immunosuppressive therapy is effective in approximately one-third of refractory patients, but often relapses occur, requiring maintenance
therapy with potentially mutagenic drugs...