The causes and pathogenesis of thrombocytopenic purpura
Last reviewed: 19.10.2021
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The causes of thrombocytopenic purpura are not exactly established; Among the precursor to the development of idiopathic thrombocytopenic purpura factors, viral and bacterial infections (40% of cases), grafts and administration of gamma globulin (5.5%), surgery and trauma (6%); in 45% of cases, the disease occurs spontaneously without previous causes. In most patients with idiopathic thrombocytopenic purpura, the premorbid background, physical and psychomotor development do not differ from healthy children.
The term "idiopathic" refers to the spontaneous onset of the disease and the etiology that has not been identified to date.
Pathogenesis of thrombocytopenic purpura. Thrombocytopenia leads to disruption of the hemostasis in the platelet unit and promotes the development of hemorrhagic syndrome of the petechial-spotted (microcirculatory) type. Thrombocytopenia is accompanied by angiotrophic insufficiency that causes dystrophic changes in the endothelium of small vessels and capillaries and leads to a decrease in the resistance of the vascular wall and an increase in its porosity for erythrocytes. This is manifested by small-point hemorrhages (petechiae) in places with higher hydrostatic pressure (lower extremities); the number of petechiae can be easily increased using the compression of the extremities by a tourniquet.
For hemorrhagic syndrome with idiopathic thrombocytopenic purpura, long bleeding from small vessels is typical, due to the inability of platelets to form a platelet plug at the sites of endothelial damage. Significant changes occur in the vascular wall and under the influence of the pathoimmune process. Because of the generality of antigenic structures of platelets and endothelial cells, endotheliocytes are destroyed by antiplatelet antibodies, which intensifies the clinical manifestations of hemorrhagic syndrome.
In the pathogenesis of idiopathic thrombocytopenic purpura, immunopathological synthesis of lymphocytes with spleen antiplatelet autoantibodies (IgG), which are fixed on various receptors of platelet and megakaryocyte membranes, is key, which confirms the pathogenic nature of the disease and the hypothesis of primary dysfunction of the lymphoid system in idiopathic thrombocytopenic purpura. Due to the autoimmune process, platelets lose adhesive-aggregation properties and quickly die, are absorbed by mononuclear cells in the spleen, and in more severe cases - in the liver and other organs of the reticuloendothelial system ("diffuse" type of sequestration). With a "diffuse" type of platelet sequestration, splenectomy is not effective enough. The half-life of their disappearance is half an hour or less.
With idiopathic thrombocytopenic purpura, the number of megakaryocytes in the bone marrow, although significantly increased, but they differ in functional immaturity (the number of immature forms increases, and the functionally active ones decreases).