Idiopathic thrombocytopenic purpura in children: diagnosis and management

In children, the term idiopathic thrombocytopenic purpura (ITP) has been loosely applied to at least four conditions; postviral thrombocytopenia, "true" idiopathic thrombocytopenia in which no precipitating factor or associated illness can be found, thrombocytopenia associated with other autoimmune syndromes and drug-induced immune thrombocytopenia. Patients initially thought to have "true" ITP may later develop lupus erythematosus or hemolytic anemia and hence move from one category to another. In 1951 Harrington demonstrated an antiplatelet factor in the serum of patients with ITP. Later this factor was proven to be an antibody of the IgG class and to be present in the blood of all four types of patients. Platelets lightly coated with antibody are sequestered and removed by the reticuloendothelial system in the spleen while more heavily coated platelets may be removed in the liver.2-4 The spleen further contributes to the thrombocytopenia by producing platelet antibodies.5-7 Recently Wybran and others8-10 have shown that cell-mediated immunity to autologous platelets may also be a factor in the pathogenesis of some cases of ITP. In view of the obvious association of ITP and altered immune mechanisms some authors have suggested the term ITP be changed to immunological or immunogenic thrombocytopenic purpura.11, 12 Karpatkin, Garg and Siskind recommend that if a platelet antibody can be demonstrated in the absence of associated disease, the term autoimmune thrombocytopenic purpura (ATP) be applied.13 Since not all patients have demonstrably altered immunity and since the cause of autoantibody production is unclear, we think the term idiopathic thrombocytopenic purpura should be retained at least for those cases in which the precipitating cause (virus or drug) cannot be identified.