Which of the following is not true about idiopathic thrombocytopenic purpura?
Ans. is 'a' i.e., Antibodies of IgM class I dopathic thrombocytopenic purpura :? There are two clinical subtypes of primary I.T.P, acute and chronic both are autoimmune disorders in which platelet destruction results from formation of antiplatelet antibodies. Pathogenesis Chronic ITP is caused by the formation of autoantibodies against platelet membrane glycoproteins most often Hb-lIla or Ib-IX. In overwhelming majority of cases the antiplatelet antibodies are of the .IgL, class. The mechanism of platelet destruction is similar to that seen in autoimmune hemolytic anemias. Opsonized platelets are rendered susceptible to phagocytosis by the cells of the mononuclear phagocyte system. The spleen is the major site of the destruction of platelets. Pathology The principal morphologic lesions of thrombocytopenic purpura are found in the spleen and bone marrow but they are not diagnostic. The point to stress is that despite the increased destruction of platelets in spleen, the spleen size remains normal. On histological examination there is congestion of the sinusoids and hyperactivity and enlargement of the splenic follicles manifested by the formation of prominent germinal centres. Sometimes scattered megakaryocytes are found within the sinuses and sinusoidal walls. This represents a very mild form of extramedullary hematopoiesis. These splenic findings are not sufficiently distinctive to be considered diagnostic. Bone Marrow Bone marrow reveals a modestly increased number of megakaryocytes. These findings are not specific for autoimmune thrombocytopenic purpura, but merely reflect accelerated thrombopoiesis, being found in most forms of thrombocytopenia resulting from increased platelet destruction. The impoance of bone marrow examination is to rule out thrombocytopenias resulting from bone marrow failure. A decrease in the number of megakaryocytes goes against the diagnosis of I.T.P.
Antibodies of IgM class
Autoantibodies to Gp IIb/ Ilia or IB IX
Increased megakaryocytes in bone marrow
Spleen is normal in size