Immune Thrombocytopenia: A Complex Autoimmune Disease

Immune thrombocytopenia (ITP) has been the prototypic autoimmune disease since platelets can be measured easily and frequently to document disease status. Over hundreds of years, cases have been described by many luminaries but the immunologic basis was provided by Harrington et al. when plasma from patients with ITP was infused into normal controls. Most (but not all) had their platelets drop in a dose-dependent fashion. Shulman at the NIH carried on this work exploring many factors, for example, the effects of steroids to blunt recipient thrombocytopenia. He furthered understanding of the immunologic underpinnings of ITP by describing transient neonatal thrombocytopenia in infants of mothers with ITP. These findings initiated the era of measuring platelet antibodies which seemed wonderful until the high rate of false positives was recognized. Further methodological improvements of antiplatelet antibody testing have been made but currently, there is no general recommendation to measure platelet antibodies in patients. The failure to measure platelet antibodies in a way related to disease course is not an indication that ITP is not an autoimmune disease. This chapter will describe our current understanding of the complicated pathophysiology of what had initially seemed to be a "simple" autoantibody disease.