Autoimmune thrombocytopenic purpura (ATP), also referred to as idiopathic thrombocytopenic purpura, is a common clinical disorder of immune regulation seen more often in females than males (3: 1). Autoantibody (usually 7S IgG) is produced against platelets and, possibly, megakaryocytes, leading to the phagocytic destruction of these cells. The resultant thrombocytopenia induces purpura and haemorrhage if the platelet count reaches a critical level (usually< 30000/μL). The disease is often complicated by the transfer of anti-platelet antibody across the placenta with resultant neonatal thrombocytopenia, purpura, and haemorrhage. Because of the immunological nature of the disorder, in which the host’s immune system destroys the host’s platelets (figure 1) I and others recommend that the term “idiopathic” be replaced by “autoimmune”. 1 Acute and chronic forms of ATP are recognised. Acute ATP occurs most often in children, and in 50% of cases it follows a seasonal (winter/spring) viral illness. The interval between the infection and the purpura averages 2 weeks. The disease typically lasts for 1–2 months and rarely persists longer than 6 months. The sex ratio in acute ATP is 1: 1. Although the acute disease is considered a milder disorder with a better prognosis than chronic ATP, 27 deaths have been reported out of a total of 709 cases not treated with steroids. 7–28% of such children develop chronic ATP. The incidence of chronic ATP is about 10 in every 100000, and is most often seen in adults; it may last for years or even indefinitely. Apparent remissions are usually remissions of purpura only. The platelet count remains at one-third to one-half the normal value of 150000 (or more)/μL, but can drop precipitously to dangerous levels (< 10000/μL) after a viral infection. Some patients have been followed up with chronic ATP for 30 years. 2

Signs and symptoms The degree of thrombocytopenia required for haemorrhage varies between 10000 and 30000/μL, and is probably dependent upon such factors as platelet age (greater functional capacity of early-released large stress platelets, 3 or megathrombocytes4), antiplatelet antibodybinding to critical functional receptors, and capillary vessel integrity. The bleeding is predominantly dermal and mucosal, and bleeding into the skin with pinpoint haemorrhage (petechiae), particularly in dependent areas where there is increased capillary pressure (ie, the legs) is common. The petechial purpura may become confluent and present as ecchymoses. The common mucosal areas are nasal, buccal, gastrointestinal, and uterine. Conjunctival and retinal haemorrhages are rare. There is